Electricity for HVACR [1 ed.] 0135125340, 9780135125342

Table of contents :
Cover
Acknowledgements
About the Author
Table of Contents

Citation preview

■

Joseph Moravek

Electricity for HVACR

JOSEPH MORAVEK

Nance Universal HVACR Technical School, Beaumont, Texas

PEARSON Boston Columbus Indianapolis New· York San Francisco Upper Saddle River Amsterdam Cape Tovvn Dubai London Madrid Nlilan Nlunich Paris Montreal Toronto Delhi Mexico City Sao Paulo Sydney Hong Kong Seoul Singapore Taipei Tokyo

Editorial Director: Vernon R. Anthony Senior Acquisitions Editor: Lindsey Gill Editorial Assistant: Nancy Kesterson Director of Marketing: David Gesell Senior Marketing Coordinator: Alicia \:Vozniak Marketing Assistant: Crrstal Gonzalez Program Manager: tvlaren L. l\.'1iller Operations Specialist: Deidra SkahiJJ Development Manager: Robin C. Bonner for Aptara·:Bl, Inc. Development Editor: Leslie Lahr Senior Art Director: Diane Y. Ernsberger Art Director; Jayne Conte Cover Designer: Suzanne Behnke Permissions Researcher: lvfaria Siriano Image Permission Coordinator: tv'like Lackey Cover Art: Fieldpiece lnstrwnents Lead Media Project Manager: April Cleland Full-Service Project Management: Peggy Kellar for Aptara®, Inc. Composition: Aptara®, Inc. Printer/Binder: R. R. Donnelly, \Villard Cover Printer: Lehigh-Phoenix Color/Hagerstown Text Font: Minion

Credits and acknowledgments borrowed from other sources and reproduced, with permission, in this textbook appear on the pages 573-577. lvlicrosoft® and \Vindows® are registered trademarks of the lvlicrosoft Corpora ti.on in the U.S.A. and other countries. Screen shots and icons reprinted with permission from the Microsoft Corporation. This book is not sponsored or endorsed by or affiliated with the Jviicrosoft Corporation. Copyright© 2014 by Pearson Education, Inc. All rights reserved. l\.1anufactured in the United States of America. This publi­ cation is protected by Copyright, and permission should be obtained fro111 the publisher prior to any prohibited reproduction, storage i11 a retrieval system, or transmission in any fonn or by any means, electronic, mechanical, photocopying, recording, or likewise. To obtain pennission(s) to use material from this work, please submit a written request to Pearson Education, lnc., Permissions Department, One Lake Street, Upper Saddle River, New Jersey 07458, or you may fax rour reques. t to 201-236-3290. 1v1any of the designations by manufacturers and sellers to distinguish their products are claimed as trademarks. 'vVhere those designations appear in this book, and the publisher was aware of a trademark claim, the designations have been printed in initial caps or all caps. Library of Congress Cataloging-in-Publication Data

Moravek, Joseph. Electricity for HVACR/Joseph ivforavek.-First edition. pages cm Includes bibliographical references and index. ISBN-13: 978-0-13-512534-2 ISBN-10: 0-13-512534-0 l. Air conditioning-Electric equipment. 2. Heating-Electric equipment. 3. Ventilation-Electric equipment. 4. Refrigeration and refrigerating machinery­ Electric equipment. 5. Ek.ctric circuits. I. Title. TK4035.A35Iv167 2013 62 l.3 I 9'24 -dc23 2013009166

10 9 8 7 6 5 4 3 2 1

PEARSON

ISBN I3: 978-0- I 3-512534-2 ISBN 10: 0-13-512534-0

This book is dedicated to my wife, Martha E. Moravek,

who tolerated my absence for the period while I was working on this project

This page intentionally left blank

Preface This book \Vas written to help a person \vith no electr.i­ cal experience or training to understand the operation of HVACR electrical circuits. This 1naterial does not get into the theory of electrical circuits; instead, it provides the fun­ damental information needed to understand and repair an HV ACR system. Therein lies the real goal of this book: to teach the reader ho\v to correctly diagnosis and solve elec­ trical problems. As an aspiring HVACR technician, you will never know' it all. There is always something nev: and inter­ esting to learn. If you are a lifetime learner, you ,vill like our profession. Let's look at some of the features and benefits of Electricity for HVACR.

HOW THE TEXT IS ORGANIZED Electricity for HVACR is divided into 28 progressive units. It is designed with the spiral learning concept, \vith each ne\v unit building on content learned from the previous unit. The first units begin · with funda1nentals such as defining tern1s used in our industry. A unit on the safe use of instruments addresses ho·w to use diagnostic tools and instrun1ents safely. This includes information on purchasing a qual.ity and safe voltage­ measuring product. The first half of the book includes 1nany units that discuss the co1nmon co1nponents found in HVACR systems. These units describe the operation of the electrical components and ho,v to troubleshoot them. Next, the n1iddle content discusses the symbols and components that make up an electrical diagrain. The reader is slo\vly taken through the process of understanding electri­ cal diagrams. Many examples are used to explain the operat­ ing sequence of diagrams. Unit 16 covers the "green" electronically co1nmutated motor (ECM). This motor represents a great advance in technology. Because this ne,v, advanced technology is not 'vvell understood, the goal of the unit is to help the learner understand the operation and troubleshooting of ECI'vfs. Units 21 through 24 describe the sequence of operation for air conditioning, gas heat, electric heat, and heat pump systems, respectively. These units apply what was learned in the preceding 20 units.

The final four units describe the all-i111portant trouble­ shooting process. Unit 25 discusses ho,v to get started. It offers some basic techniques to help the reader apply troubleshooting skills at the beginning of the search for the problem. Ultimately, this is the goal of this book: learning how· to troubleshoot and repair. If a student-tech cannot find and repair an H\TACR problem, then this book \\rill help him or her "figure it out."

IMPORTANT FEATURES OF THE TEXT What You Need to Know Each unit opens \Vith learning objectives entitled "What You Need to Know·." These objectives serve as a unit outline and, more in1portantly, provide the student ,vith attainable learn­ ing goals.

summary Each unit concludes with a Summary that recaps and high­ lights the unit content.

Review Questions Review Questions found at the end of each unit challenge readers to test their understanding of the reading. The ques­ tions cover each i1nportant aspect of the unit's content. Some questions require identification of HVACR components, use of troubleshooting skills, and tracing of ,viring diagrams.

Tech Tips Tech Tips provide hands-on hints based on the author's years of experience in the field. These tips offer the new (and experienced) technician practical insights into key HVACR components, their installation, and troubleshooting techniques.

Safety Tips Safety Tips offer crucial, and sometimes lifesaving, point­ ers for the technician in the field. A long productive career V

vi

PREFACE

in HVACR requires stringent safety practices. Accident and injury prevention is tantamount to good ,vorkmanship­ look after yourself and those around you.

Green Tips Green Tips highlight nevv technologies and components being used in the field that have been designed to save electricity. These tips offer the new technician a chance to become familiar with some of the latest advancements in the H\TACR industry.

sequence of Operation Boxes Sequence of Operation boxes describe, step by step, the oper­ ation of specific pieces of equipn1ent. The numbered steps are tied to a numbered diagran1, ,vhich creates a visual learn­ ing experience for the student.

Troubleshooting Boxes Troubleshooting boxes offer instruction on ho,v to trouble­ shoot an electrical problem, one step at a time. To aid student comprehension of the troubleshooting process, each num­ bered step of instruction is matched to a nwnbered photo­ graph of actual equipment or a nun1bered diagram.

Examples Exa1nples are offered to help students ,vork with the forn1ulas and calculations used in the HVACR field. Examples present a real-world problem and then ,valk the student through the steps of the solution.

service Ticket The Service Ticket presented at the end of each unit puts the student in an on-the-job situation. Each scenario involves a problem that requires the reader to use the concepts and techniques presented in the unit to arrive at a satisfactory res­ olution. The scenario includes an evaluation and assessment of the problem, the 1nost probable cause, and a solution that satisfies both the customer and the technician's employer.

Electrical Diagrams Electricity for HVACR has n1any special features, but the 14 enlarged electrical diagrams that are included ,,vith the book make it stand out fron1 other HVACR books. These are referred to as Electrical Diagram ED-1, ED-2, etc. It can be difficult to read textbook diagrams because they are limited by the size of the page. Printing a nvo-page diagram on facing pages is possible, but the break between the pages 1nakes the diagrains difficult to follo,v, ,vhich creates a problem for the user. For these reasons, we have included 14 enlarged electrical

diagrams that are much easier for the learner to follo,v dur­ ing discussions by the instructor or ,vhen ·working ,vith the detailed inforn,ation in each unit. The electrical diagrams are actual diagrams one might come across in the field. The diagrams cover the gamut of the I-IVACR field, including gas heat, electric heat, and heat pumps; and residential, con11nercial, and industrial air conditioning systems, including chilled vvater systen1s. The electrical diagrams were selected to represent all areas of HVACR, yet they are basic enough to be understood for the entry-level technician.

COMPREHENSIVE SUPPLEMENT PACKAGE Download Instructor Resources from the Instructor Resource Center To access supplementary materials online, instructors need to request an instructor access code. Go to w,V\v.pearson­ highered.com/irc to register for an instructor access code. Within 48 hours of registering, you ,,vill receive a confirming e-n1ail including an instructor access code. ()nee you have received your code, locate your text in the online catalog and click on the Instructor Resources button on the left side of the catalog product page. Select a supplen1ent, and a login page ,vill appear. Once you have logged in, you can access instructor n1aterial for a!J .Pearson textbooks. If you have any difficulties accessing the site or dovmloading a supplement, please contact Customer Service at http://247pearsoned. custhelp.con1.

Instructor's Solutions Manual, ISBN-10: 0-13-512537-5 Includes solutions to the end-of-unit questions and the lab n1anual.

PowerPoint Slides, ISBN-10: 0-13-302725-2 Includes a comprehensive, colorful image bank and Po·werPoint presentations for all units.

Lab Manual, ISBN-10: 0-13-512536-7 The printed lab manual offers basic coverage of all of the major lessons in each unit.

MyTest, ISBN-10: 0-13-512576-6 MyTest is a comprehensive set of test questions that match the key objectives for each unit.

Acknowledgments Without the help of those listed here, the quality of the product you are about to explore \Vould have suffered. The HVACR professional must thank everyone listed here for their support of our industry. Their tin1e, insights, and sug­ gestions helped make this book better and stronger.

Dave DeRoche St. Clair College Windsor, Ontario

Vernon Anthony Pearson

Michael W. Falvey Copiah-Lincoln Co1nmunity College

Dan Trudden Pearson

Luther Gardner Son1erset County Technology Center

Larry Giroux Giroux Air Conditioning Training

Nicholas Grie,vahn Northern Michigan University

Roger Stuksa Curtis .tv1cGuirt

Patrick Heeb Long Beach City College

Jeff Zinsmayer Zinsmayer Design and Construction

John Hohman EDE1VIPCO

Thanks to all of the HVACR contractors who answered my polls and offered suggestions to n1ake this a prenlium product. Many reviewers improved this product \\rith ideas, sug­ gestions, and content. They are:

Ja1nes Janich College of DuPage

Tin1othy Andera South Dakota State University Douglas Broughman Augusta Technical College Edv,ard A. Burns Harrisburg Area Community College

Patrick F. Duschl Fortis College Cincinnati

Rick Lutz Red Rock Comn1unity College Christopher .tvlohalley Genteq Michael .tvlutarelli Lehigh Carbon Comn1unity College Paul Oppenheim Un i.versity of Florida

Danny B. Burris Eastfield College of Dallas County Conununity College District

Thomas E. 0\ven, Jr. Sullivan College of Technology and Design

Thomas Bush South Florida Con1munity College

Jacky Skelton Arkansas Northeastern College

Victor Cafarchia El Can1ino College

Samuel Shane Todd Ogeechee Technical College

Michael D. Covington Sullivan College of Technology

Mark \Tan Doren Ivy Tech Community College

viii

ACKNOWLEDGMENTS

Freddie Williams Lanier Technical College

Air-Conditioning, Heating, and Refrigeration Institute (AHRI)

I vvould like to thank the follovving people for their con­ tributions to,.vard making this work a professional benefit to the H\TACR profession. First, T vvant to thank Pearson for selecting me to co1n­ plete this important project. I want to thank Dr. John Hohman, Ph.D., for his contribution to writing several high-performance units. Dr. Hoh1nan also offered good advice and support prior to starting the project. My ,-vife, Martha Moravek, developed and organized the important glossary. Others ·who offered continued support and 1nentoring were Larry Giroux of Giroux Training, and Chris lv1oha1ley of Genteq and Roger Stuksa, an independent HV ACR contractor. I want to thank the Aptara, Inc., Production Department for making this product so appealing and useful to the student.

Alco Products Allen Bradley Allied Air Enterprises American Standard AmRad Engineering ARESCO Bolt Depot Carrier Corporation Copeland Co1npressors Don Cra·wshaw, HVAC/R Productions Diversitech Edison Electric Institute En1erson Climate Technologies Fasco Motors

SPECIAL THANK YOU I ,,vant to express special appreciation to Leslie Lahr of Aptara, Inc., for her talents and perseverance in helping me to the goal line. lt was difficult and she ,vas the biggest supporter and n1otivator in bringing this ,,vork to fruition. Her editing skills brought out the best in this project. Leslie does not have an air conditioning background, ·which helped. If she could understand what ,,vas being conveyed, the learner should be able to do the same. Many of her suggestions, ideas, con­ cepts, and improvements are seen in every unit. The success of this project can be largely contributed to Leslie. Great job, Leslie-it was a pleasure to have ,,vorked ·with you. I hope \Ve can do another project together. Maren Miller managed to keep all of the pieces together ,vith remarkable skill. She orchestrated not only the process of building the book, but also the people needed to get the job done. Initially, Robin Bonner of Aptara Productions kept the project rolling and directed in a positive 1nanner. Thank you, Robin. The final manuscript and art content ,vere managed by Peggy Kellai-, Aptara, Inc., and Lorretta Palagi, Quantum Publishing Services, Inc. Their sharp editing skills offered final improve1nents so that we can offer the finest published product possible. It is difficult to obtain permission to use H\TACR im­ ages. Maria Siriano of Redline Ink 1net the challenge. I \Vant to recognize the contributions of the follO'wing con1panies. They provided images and granted permission to use pictures, tables, and diagrams of their fine products. These iinages are used throughout the book and supporting supplements.

Fieldpiece Instruments Fluke Corporation Genteq Giroux Air Conditioning Training Goodn1an Manufacturing Ha1npden Engineering Dr. John Hohman ICM Controls Ideal Industries Johnson Supply National Fire Protection Agency OSI-IA Pearson Production Departtnent Refrigeration Basics Reliant Energy Ritchie Manufacturing Rockwell Automation Sealed Unit Parts Con1pany (SUPCO) Siemens Sporlan Corporation Square D Tecumseh Corporation II Push bullet

ACKNOWLEDGMENTS

Thermostat Recycling Corporation

,[email protected]

3Nf

\\1WW.onsem1.com

Trane Corporation

w,....,,v.quest-comp.com

U.S. Depart1nent of Energy

York

U.S. Information Adn1inistration

Zebra Instrun1ents

Venstar \VEG

Author contact information:

Joseph Moravek [email protected]

ix

About the Author Joe Moravek has been in the air conditioning profession since 1975 when he ,,,ent to work doing heat load calcula­ tions on low·-income homes in Houston, Texas. Fron1 there he ·was en1ployed by the University of Houston's College of Technology where he ·was involved vv-ith the Texas Energy Extension Service offering energy-saving training and con­ stilting for homeovvners and small com1nercial businesses. Other related jobs included \Vorking for the City of Houston in the Energy Conservati.on Office, ·working as an HVACR technician in the Parks and Recreation Department, and \Vorking as a mechanical inspector in the Occupancy Department. During his time ,vith the City of Houston, he taught as an adjunct instructor for San Jacinto College and H.ouston Comn1unity College. Joe found his love for teach­ ing and left the municipal environment to become a full­ tin1e HVACR instructor. Joe received his master's degree in education fro1n the University of Houston in 1980.

Next, he was the lead HVACR instructor for 14 years at Lee College, in Baytown, Texas, helping to improve the quality

X

of the courses the departn1ent offered. The next challenge ,.vas at the corporate level. Joe ,.vas the first corporate training n1anager for Hunton Trane in Houston, Texas. He developed curriculum, taught classes, and improved the delivery quality of training material. His current job is as Training Director at Nance Universal HVACR Technical School in Beaumont, Texas. This vvas a new position for Nance School and for the past five years, Joe has ,.vorked to attract quality instructors and offer an exceptional curricuhun. Joe has published several books, reviewed 1nore than t\.vo dozen training W'Orks, and has published many HVACR book revie·ws. Finally, the author is kept busy \vith his consulting business, Mechanical Training Services. This work gets him involved in training, developing training, and helping solve contractors' technical. problems on the job. He is a licensed air conditioning and refrigeration contractor in Texas and conducts required continuing education classes for his fello,,v contractors. He welcomes co1n1nents on this book and can be contacted at [email protected].

contents Unit 1 What You Need to Know to Understand Electricity 1

3.12 Ho,-v Much Electricity Is Too Much? 40 3.13 Arc Flash

42

1.1 ,,vhat is Electricity?

l

3.14 \Vhat to vVear ,i\'hen l\,1easuring Voltage

1.2 Types of Electricity

2

3.15 Safety Tips from Canada 43

1.3 Electrical Tenns Used in HVACR 3

3.16 Safety Tips When Using Meters 6

1.4 Combining Volts, Amps, and Resistance

Unit 2 Ohm's Law and Circuit Operation 10 2.1 Technical Revie\-v 11 2.2 Ohn1's Lav.-, 11 2.3 How· E, I, and R Influence Each Other

12

2.4 Series Circuits 13 2.5 Parallel Circuits 13

3.17 Lockout/Tagout Procedure

2.7 Using the Ohm's La,v vVheel 2.8 Using the Watts Formula

16

4.3 Bolts, Nuts, and Washers

50

52

4.7 Electrical Tape

17

44

4.1 Wire Nuts 47 4.2 Scre\-vs 48

4.5 Nylon Straps 52 4.6 Quick Connectors

14

44

Unit 4 Electrical Fasteners 47

4.4 Nails

2.6 Combination Circuits

53

57

Unit 5 Power Distribution 59

2.9 Co1nbined ()hrn's Law and Watts Formula Wheel 18

5.1 When Did Po\-ver Distribution Start?

2.10 Calculating Resistance 19

5.2 Energy La,�, of Conversion

2.12 Resistance in Parallel Circuits

5.4 High-Voltage Distribution

20

2.13 Resistance in Series-Parallel Circuits

22

unit 3 Safe use of Electrical Instruments 26 3.1 Read the Directions!

28

3.2 Digital Multimeters

28

3.3 RlvIS 30 3.4 ,,vhat Do All Those Symbols l\.1ean? 3.6 Measuring AC and DC Voltage 3.8 Reading Amperage 3.9 Optional Features

5.5 End Use Distribution by Transforn1ers 5.6 Con1mercial Transformers 5.7 Residential Service

62

65

67

5.8 Commercial Service 72 5.9 What Is the Current Status of Electrical Use? 31

73

Unit 6 National Electrical Code® 80

33

6.2 Definitions

81

6.4 Electric Heating Equip1nent

33

6.5 Duct Heaters

36

3.11 Selecting a Safe Multi1neter

60

6.3 How to Find Information in the NEC

33

3.10 Beware of Ghost Voltage

59

6.1 The NEC at \\Tork 80

3.5 Voltmeter Function 32 3.7 Measuring Resistance

59

5.3 Electrical Distribution Terms and Abbreviations 60

19

2.11 Resistance in Series Circuits

43

83

86

6.6 Self-Contained Electric Heating Units

39 39

6.7 Motors

83

86

86 xi

Xii

CONTENTS

6.8 Compressor Motors 88 6.9 Condensing Units 88 6.10 Condensing Unit Nameplate 89 6.11 Electrical Conductors in Air Ducts 90 6.12 Sizing Conductors 90 6.13 Romex 93 6.14 Fuse Sizing 95 6.15 Branch Circuit 95

Unit 7 Electrical Installation of HVACR 101 7.1 New Installations 103 7.2 High Voltage 105 7.3 Control Voltage 107 7.4 Replacing HVACR Equipment 109 7.5 Large HVACR Systems 111 7.6 Additional Electrical Requirements 112 7.7 Installation Infonnation 115 7.8 Installation Notes 115 7.9 Electrical Checklist 117 7.10 Rewiring Equipn1ent 117 7.11 Open Wiring and Conduit J 17

Unit 8 Transformers 123 8.1 Ho,..., DoTransformers Work? 123 8.2 Types ofTransformers 124 8.3 Calculating Volt-Amps (VA) 128 8.4 Checking Input Voltage on a Transformer 129 8.5 Checking Output Voltage on aTransformer 129 8.6 ]\!foreTransformerTips 130 8.7 Wiring Transfonners in Parallel 131

Unit 9 Relays, Contactors, and Motor Starters 136

9.1 Common Features 136 9.2 Differences Among Relays, Contactors, and Motor Starters 138 9.3 Relays 139 9.4 Contactors 141 9.5 Troubleshooting Contactors 144 9.6 l'v1otor Starters 145 9.7 Electrical Diagran1s 147 9.8 Reading Electrical Diagran1s 1.49 9.9 Motor Starter Replace1nent 149

Unit 10 Capacitors 154 10.l 10.2 10.3 10.4

Capacitor Symbol 154 Capacitor Construction 154 Capacitor Operation 155 Types of Capacitors 155

10.5 How Are Capacitors Rated? 158 10.6 Troubleshooting Capacitors 158 10.7 Capacitors in Series and Parallel 160 1.0.8 Installing Capacitors 161

Unit 11 Thermostats 164 11.1 Types of Thermostats 164 11.2 Parts of aThern1ostat 166 11.3 Operating Voltage 166 11.4 Thermostat Installation 168 11.5 Thermostat Wiring 168 11.6 Summary ofTerminal Connections 171 11.7 MechanicalThermostats 171 11.8 Heating Anticipator 177 11.9 Cooling Anticipator 178 11.10 Types of MechanicalThennostats 179 11.11 Basic CoolingThermostat Hookup 179 11.12 Basic Heating ()peration 180 11.13 Touch Screen 183 11.14 ProgrammableThermostat Language 183 11.15 Programming Options 184 11.16 DummyThennostat 185 11.1 7 Thermostat Diagrams 186 11.18 General Troubleshooting Steps 188

Unit 12 Pressure Switches 192 12.1 12.2 12.3 12.4

Lo,...,-Pressure s,...,itches 192 Lo,v-Pressure S·witch Installation 195 Loss of Charge S,-vitch 195 Determining If a Lo,-v-Pressure Switch ls Defective 195 12.5 High-Pressure S·witches 199 12.6 High-Pressure S,vitch Installation 201 12.7 Detern1ining If a 1-ligh-Pressure S\vitch ls Defective 202 12.8 Dual-Pressure Svritch 204 12.9 Condenser .Fan Cycling S'.vitch 204 12.10 Oil Pressure Safety Switch 205 12.11 Troubleshooting the Oil Safety Pressure s,�ritch 207

Unit 13 Miscellaneous Electrical Components 214 13.1 13.2 13.3 13.4 13.5 13.6 13.7

Crankcase Heater 214 Troubleshooting the Crankcase Heater 214 Solenoid Valve 215 Troubleshooting the Solenoid Valve 217 Electric Unloaders 218 Troubleshooti.ng the Electric Unloader 219 Replacing the Electric Unloader 219

CONTENTS

13.8 Solid-State Time Delays 219 13.9 Troubleshooting the Solid-State Timer 220 13.10 Lockout Relay 220 13. l l Reset Relay 222 13.12 Troubleshooting the Lockout Relay 224 13.13 Hot Gas Thermostat 224 13.14 Troubleshooting the Hot Gas Thennostat 224 13.15 Line Voltage Monitor 224 13.16 Explosion-Proof Systems 225 13.17 Overload Relay 226 13.18 Troubleshooting the Overload Relay 227

Unit 14 How Motors Work 230 14.1 Before We Start! 230 14.2 Use of Meters 231 14.3 Starting Torque 232 14.4 Running Operation 232 14.5 Voltage 232 14.6 Ho,,v Do lvlotors ,i\'ork? 233 14.7 Thermal Protection 235 14.8 Nan1eplate Infonnation 237 14.9 Rated Voltage 238 14.10 Rated Load Amps (RLA) 238 14.11 Locked-Rotor Amps (LRA) 238 14.12 Frequency 239 14.13 Phase 239 14.14 Horsepower 239 14.15 RPivl Speed 239 14.16 Multispeed Single-Phase Motors 240 14.17 Insulation Class and Rated Ambient Temperature 241 14.18 Service Factor (SF) 241 14.19 Frame 241 14.20 Po,,ver Factor (PF) 243 14.21 Time Rating or Duty 243 14.22 Bearing Types 243 14.23 Service Checklist 244

Unit 15 Motor Types 248 15.l 15.2 15.3 15.4 15.5 15.6 15.7 15.8

Types of 11otors 248 Shaded Pole Motors 248 Troubleshooting the Shaded Pole Motor 250 Split-Phase Motors 251 Troubleshooting the Split-Phase Motor 253 Capacitor Start/Induction Run 1v1otors 253 Troubleshooting the Capacitor Start Motor 256 Permanent Split Capacitor Motor 259

xiii

15.9 Capacitor Start/Capacitor Run Motor 263 15.10 Hard Start Kits 265 15.11 Troubleshooting the CSCR Motor 266 15.12 How to Detennine Compressor Windings 267 15.13 Verifying CSR Terminals 267 15.14 Three-Phase l\1otors 270 15.15 Troubleshooting Three-Phase Motors 271 15.16 Dual-Voltage M.otors 272 15.17 Three-Phase Diagram 273 15.18 Motor Mounts and Accessories 275 15.19 Motor Ventilation 275 15.20 Motor Replacement and Amp Ratings 276 15.21 Motor Rotation 278

Unit 16 ECM: The Green Motor 285 16.1 16.2 16.3 16.4 16.5 16.6 16.7

Industry Standards 286 ,,vhat is an ECM? 286 ECivI \\!iring 289 Installation Setup 290 Dehumidification and Energy Efficiency 293 Constant-Torque EC.l\1 294 Troubleshooting the Variable-Speed ECM 296 16.8 Airflov, Problems 298 16.9 Motor Resistance 298 16.10 Helpful Instruments 298 16.11 The Constant-Torque ECM Checklist 299 1

Unit 17 Understanding Electrical Diagrams 308 17.1 Symbols 308 17.2 Circuit Types 311 17.3 Types of Electrical Diagrams 315 17.4 Wiring Diagrams 315 17.5 Schematic Diagrams 318 17.6 Identifiy ng the Parts of a Diagram 318 17.7 Guidelines for Reading Electrical Diagrams 325 17.8 Designing an Electrical Diagram 327 17.9 Dra\.ving a Field Diagra1n 328 17.10 Rewiring a Systen1: The Wire and Test Method 331

Unit 18 Resistors 342 18. l 18.2 18.3 18.4 18.5 18.6

The Resistor 342 Types of Resistors 342 Po,.ver Rating 343 Operating Te1nperature and Voltage 343 Tolerance 343 Calculating Resistance 343

xiv

CONTENTS

Unit 19 Fundamentals of Solid-State Circuits 347

Unit 23 Electric Heating Systems 437

19.l 19.2 19.3 19.4 19.5 19.6 19.7 19.8

23.l Electric Heating System Types 438 23.2 Electric Baseboard Heat 440 23.3 Electric Backup Heat 441 23.4 Electric Furnace 441 23.5 Common Components of an Electric Heater 23.6 Heat Strips 443 23.7 Sequencers 444 23.8 Overcurrent Protection 446 23.9 Fusible Links 447 23.10 Thermal Overloads 447 23.11 Miscellaneous Con1ponents 448 23.12 Wiring Requiren1ents 449 23.13 Operation 449 23.14 Efficiency Check 450 23.15 Three-Phase Heat Strips 451 23.16 Basic Troubleshooting Checklist 452

Capacitors 347 Diodes 348 Transistors 349 Integrated Circuits 349 Rectifiers 349 \Taristors 350 Microcontrollers and M.icroprocessors 351 Circuit Boards 351

Unit 20 Taking the Mystery Out of Circuit Boards 355

20.1 20.2 20.3 20.4 20.5 20.6 20.7

Construction of Circuit Boards 355 Understanding Circuit Boards 356 Five-Minute Time-Delay Circuit Board 356 ® Tech.Assist Circuit Board 361 Troubleshooting a Circuit Board 364 Troubleshooting a Circuit Board Using a Diagram 366 Ivlore Practice Vl7ith Circuit Boards 368

Unit 21 Air Conditioning Systems 372 21.1 21.2 21.3 21.4 21.5 21.6 21.7

Basic Air Conditioning Systems 372 Windo.v Air Conditioners 372 Ivlultispeed Fan Motors 376 Po.ver for Window· Units 376 Package Air Conditioning Syste1ns 378 Split Air Conditioning Systems 378 Commercial Air Conditioning Systen1s 380

Unit 22 Gas Heating Systems 391 22.1 Classifying Gas Heating Syste1n Types 391 22.2 Venting Syste1ns and Efficiency 392 22.3 Gas Furnace Con1ponents 394 22.4 Door S.vitches 394 22.5 Gas \Talves 395 22.6 Inducer Fan Assembly 396 22.7 Hot Surface Igniters 396 22.8 Fla1ne Sensors 398 22.9 High Limit $,-\'itches 400 22.10 Flame Rollout S,vitches 401 22.11 Circuit Boards 403 22.12 Blo,�rer Motor Assen1bly 404 22.13 Lo,v-Efficiency Gas Furnace Operation 404 22.14 High-Efficiency ()peration 409 22.15 Basic Troubleshooting Procedures 412 22.16 Troubleshooting of High-Efficiency Systems 413 22.17 Additional Revie,v of Gas Furnace Operation 422 22.18 Tracing More Diagran1s 428

443

Unit 24 Heat Pump Heating Systems 454 24.1 24.2 24.3 24.4 24.5

Heat Pump Types 454 Electrical Com . ponents 455 Reversing Valve 456 Heat Pump Thermostat 460 Printed Circuit Board for Heat Pump Applications 461 24.6 Loss of Charge Pressure Switch 463 24.7 Defrost Controls 463 24.8 Causes of Inco1nplete Defrosting 469 24.9 Crankcase Heater 469 24.10 Hard Start Kit 469 24.11 Auxiliary and E1nergency Heat 469 24.12 Heat Pu1np Cycles 470 24.13 Heat Pump Wiring 473 24.14 Consumer Choices 480 24.15 Basic Troubleshooting Checklist 482

Unit 25 How to Start Electrical Troubleshooting 489 25.1 25.2 25.3 25.4 25.5

What is Troubleshooting? 489 Quick Checks for Air Conditioning Proble1ns 489 Heating System ACT Troubleshooting 491 Use Your Senses 491 Understanding Basic Troubleshooting by Using a Voltage 1/f eter 492 25.6 �1ethods of Electrical Troubleshooting 495

Unit 26 Basic Troubleshooting Techniques 503 26. J Kno·w What ls Happening 503 26.2 Troubleshooting an Air Conditioning Syste1n 504

CONTENTS

26.3 Using Equipment Diagnostics 506 26.4 Troubleshooting Electric Heating Systems

507

26.5 Troubleshooting Heat Pump Heating Systems 513 26.6 Troubleshooting Fossil Fuel Heating Systems 26.7 Using a Flowchart

514

514

26.8 Troubleshooting Table

516

Unit 27 Advanced Troubleshooting 519 27.1 RevieVlr of Troubleshooting Steps 519 27.2 Manufacturers' Notes Explained 521 27.3 Check the Capacitor 527 27.4 Check the Voltage 527 27.5 Locked Rotor An1ps (LRA) 527 27.6 Installing a Hard Start Kit 529 27.7 Overheating Problen1s 530 27.8 Before Conde1nning 530 27.9 Voltage and Cturent Imbalances 531 27.10 How· to Locate the Source of Current Imbalance 533 27.11 lvlegohm Testing as a Troubleshooting Tool 533 27.12 Not All Electrical Failures Are Electrical Problems 535 27.13 The Mystery Nuisance Trip 536

XV

Unit 28 Practical Troubleshooting 542 Service Call 1: Hopscotch Practice 542 Service Call 2: Inadequate Heating 545 Service Call 3: "No Cooling" Call for a 5-Ton Package Unit 547 Service Call 4: Inadequate Cooling 548 Service Call 5: Lack of Cooling 549 Service Call 6: No Cooling-Short Cycling Compressor 551 Service Call 7: No Heating 552 Service CalJ. 8: No Chilled Water from Con1pressor l 553 Service Call 9: No Chilled Water fro1n Compressor 2 556 Service Call 10: No Chilled Water Pump Operation 556 Service Call 11: No Cooling, Short Circuit 558 Service Call 12: First Steps 559 Glossary

560

Appendix A: Abbreviations and Acronyms Appendix B: HVACR Formulas

Photo Credits Index 578

573

569

567

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UNIT 1

What You Need to Know to Understand Electricity WHAT YOU NEED TO KNOW After studying this unit, you will be able to: Describe the components of electricity. 2. Explain how alternating current (AC) and direct current (DC) electricity work. 3. Define important electrical terms and symbols used in HVACR. 1.

This unit provides you ·with the most basic electrical informa­ tion required to understand ho,v the electricity in our equip­ ment vvorks. As you progress you w-ill notice that this book does not go into deep theory applications such as ho,v aton1s 0rk or electrical theory. We are not trying to turn you .into an electrical engineer. You do, ho\vever, need to understand HVACR electric circuits so that you can troubleshoot and re­ pair systems. Our goal is to provide you "vith knowledge about the basics of electricity and to offer practical infonnation that you can use on your job as a professional technician. This unit is i1nportant because electrical defects in HV ACR equipment are the 1nost conunon problems you ""'ill encounter. To begin, you need an understanding of the terms used in the HVACR profession. This ·will help you communicate \\'ith other HVACR professionals as ,vel1 as your clients. Electrical terms and definitions \\1ill be used throughout this textbook. You \Vill notice in HVACR electricity that so1ne terms have the same definition. For example, the word volt can be used to refer to potential difference, electrical pres­ sure, electrical force, or the abbreviations E or V. Also, con­ sider the term electrical diagran1s. Different names may be used for electrical diagrams, but they are essentially the same thing. Electrical diagrams are also called ,v.iring diagrams, schematic diagrams, ladder diagran1s, and connections dia­ grams. Throughout this book, we \\,.iJJ present you ,vi.th all of the different terms used in the electrical side of our profes­ sion. Our intention is not to confuse you, but to sho\v that different terms are used to represent the same thing. 7

in Figure 1-1 by the movement of electrons in a ·wire. Current flo,v creates a n1agnetic field in the ,vire. The magnetis1n in the ,vire can be designed to move motors, operate svvitches, and do other \Vork in an HVACR system. Figure J--2 sho\VS tbat voltage is the pressure pushing the current flow. The top illustration compares water pres­ sure to voltage pressure. ,vater pressure can be compared to voltage (electrical pressure) and \\Tater flo\V can be compared to electron flo,.v. The greater the pressure developed by the chilled ,.vater pun1p, the greater the pressure in the piping system. The n1iddle and botto1n diagrams show voltage pres­ sure. The higher the voltage, the greater the voltage pressure. The greater the electrical pressure, the higher the voltage in the ,vire. If the voltage pressure is too low, electron flo,v ,.vill not occur.

\\

Figure 1-1 The flow of electrons is known as current flow. PUMP

1----u---1�-----------',-:=.� CHILLED

-i-�

\VATER

COIL (LOAD)

ELECTRIC LOAD

ELECTRIC LOAD

1.1 WHAT IS ELECTRICITY? Electricity is the flo\\7 of electrons between atoms in co1n1non

\\rire materials such as copper and aluminum. The flow of electrons is kno,vn as current flow. Electron flov; is illustrated

Figure 1-2 water pressure compared to voltage pressure. The gauges in the middle and lower images show that the higher the voltage, the greater the voltage pressure.

2

UNIT 1

Figure 1-5 Electrons flow in only one direction with direct

current. The DC can either be positive or negative.

1.2 TYPES OF ELECTRICITY

Figure 1-3 This illustration of a copper atom shows that the

first three inner electron energy levels of the copper atom are full, but the outermost level has only one electron. The single electron is the free electron that will be transferred between atoms to create what we know as electricity.

The atom is constructed of neutrons, protons, and elec­ trons as illustrated in Figure 1-3. The neutrons and protons are stable co1nponents and stay linked ,vithin the core of the ato1u. Free electrons can be found around the outer shell. A good conductor of electricity \.Vill have one or more free electrons in the outer shell. These free electrons move benveen atoms and create the current flo,v, as sho,vn in Figure 1-4. Electron flo,.v occurs as a chain reaction. Notice ho,-v the electrons are transferred in the outer shell of this atom. The greater the number of free electrons, the greater the current flow. This transfer of electrons results in ,.vhat v,,e call electric­ ity. Materials kt1ovvn as conductors have many free electrons in the aton1's orbit that are easily transferred between aton1s. Conductors used in H\TACR equipment are normally cop­ per "''ire. Insulators have fe,v or no free electrons to share; therefore, they resist electron or current flow. Rubber and glass are good insulators.

•

as a chain reaction.

SAFETY TIP Knowing the correct hertz for a motor or other electri­ cal component is important. Values of 60 and 50 Hz are commonly found around the world. Sixty hertz is normally found in the Western Hemisphere in North and South America. Installing a motor with the wrong hertz rating may damage a motor, so be aware that 50 Hz mo­ tors are made in the United States and sometimes find their way into the supply stream. Hertz or cycles is one of several electrical characteristics you should check when changing an electrical device.

•

•

Figure 1-4 Electron flow occurs

There are t,vo types of electricity: direct current (DC) and alternating current (AC). An example of direct current is battery voltage. Direct ctu-rent reaches its level of voltage and stays at that point as illustrated in Figure 1-5. It flovvs in only one direction and can be positive or negative, depending on ho,v the DC voltage is hooked in to the circuit. As seen in Figure 1-6, alternating current varies as posi­ tive and negative around a zero center voltage. The alternations occur 60 ti1nes a second. The com­ plete positive and negative cycle is called the hertz (Hz) or cycle. Hertz determines the speed of a 111otor. The higher the hertz, the faster the motor's revolutions per minute (RPM). Note that 50-Hz alternations are used in some countries. Alternating current is the most co1n1non po\'\1er source found in HVACR equip.ment. Direct current circuits may be found on circuit boards, but troubleshooting individual co1nponents on a circuit board is not usually practiced. Checking DC voltage is most likely done to check battery voltage.

. ..

WHAT YOU NEED TO KNOW TO UNDERSTAND ELECTRICITY MANY ELECTRONS

3

FE�'ER ELECTRONS

•• 11, ..

Figure 1-6 In alternating current the direction of electron

flow reverses at regular intervals. These variations are used to change the magnetic field in a component, which helps move motors and switches.

1.3 ELECTRICAL TERMS USED IN HVACR To understand the terms used in our profession, \Ve must de­ fine them in simple tenns. This section defines each term and give an example that relates to the definition. It is in1perative for you to kno,-v these tenns so that you can communicate problems and issues ¼rith the customer and your supervisor. Using the ,vrong tenn can create a misunderstanding that may lead to confusion and ti1ne lost on the job. Learn the follO'wing terms and use them as part of your professional language: Electron: An electron is the part of an atom that changes position from atom to atom, which creates cur­ rent flo,v. To be specific, the 1novement of electrons is current flow. Volt: The term volt or voltage refers to the pressure that pushes electrons through a circuit. The greater the pres­ sure, the higher the voltage. The term volt is also stated as potential difference, electromotive force (E:tv1F), V, or E. Common voltages used in HVACR are 24, 120, 208, 240, and 480 V. A much higher voltage is possible on larger systems. Control voltage: Control voltage is the electrical section of the HVACR system that n1anages the on and off cycles. A thermostat is usually placed in the control voltage cir­ cuit. The thermostat turns the system on and off to satisfy the custon1er's desired temperature setting. The control

Figure 1-7 current flow or electron exchange is slowed

down as resistance is increased. Note that many electrons are available on the left side of the restriction or load. The restriction or load reduces the electron flow as evidenced by fewer electrons flowing on the right side.

voltage in an air conditioning unit is normally lo,ver than the system supply voltage. Common air conditioning control voltages use 24 or 120 VAC. S01ne air condition­ ing systen1s also use low-voltage DC signals. Ampere: An ampere or amp is a measure of electron 1noven1ent in a circuit. The greater the electron move­ ment, the higher the amperage in a circuit. The term an1pere is also stated as amp, current flo,-v, and inten­ sity and is abbreviated as A or I. Amperage may be ,-vhole numbers or decimals such as 0.1, 0.01, 0.001, or 0.0001 A. The lo,\rer arnperage 1neasurements are known as milliamps or 1nicroamps. One n1illia1np is equal to one one-thousandth of an amp. One micro­ a.1np is equal to one one-millionth of an amp. \Tery lo,,v amperage is used in gas heating and other control circuits. Resistance: Resistance is the force that slows do,vn the flo¼' of electrons in a circuit, as illustrated in Figure 1-7. Resistance may be a matter of an undersized \Vire or a wire that does not conduct electrons easily. The greater the resistance, the lo,ver the electron or amp tlo,v in a circuit. The term resistance is also stated in ohms and is abbreviated vvith the letter R or the Greek letter on1ega, !1. Glass, rubber, and plastic are good insulators and stop current flo,-v. Watt: The term watt is a reference to the power con­ sun1ed by a circuit. The ,-vatt is the rate of doing ,vork. A watt, or 1vattage, is calculated by n1ultiplying the voltage by the an1perage as follo,vs: Watt

=

V X I or Watt

=EX

I

The ,vatt is used by utility con1panies to bill for electric­ ity and is used by technicians to determine if the correct ,-vattage is being dra,vn by a circuit, especially an electric heat circuit. The term watt or wattage is also kno'rvn as po,,ver and is abbreviated W or P. Load: A load is a co1nponent that has resistance to electron flow. Examples of .loads in HVACR equip1nent are a motor or electric heating element. Figures l -8A. and 1-8B sho,v conunon loads found in our profession.

WHAT YOU NEED TO KNOW TO UNDERSTAND ELECTRICITY

I

HEATERS

\

5 AivlPS

5

Figure 1-12 This is a series circuit with four heaters as loads. The total amp draw is 5 amps. All points in this series circuit have a 5-A current flow.

ELECTRON FLOW TOTAL Al'vfP DRA\V 1S5A

E= l.lOV 5AMPS ELECTRON FLO\\'

I

HEATERS

L, TOTAL AMP 110 V DRAW 1S 10.t\

---

"

'

\

,

\

IA

2A I/

LIGHT BULB

/,

I

\

\

--'

FAN

l'vlOTOR

Figure 1-13 This is a parallel circuit with four loads. The 11 o-v power supply is applied across each load. The total amperage would be 10 amps if the amp draw in the light bulb is 1 A, the amp draw of the fan motor is 2 A, and the amp draw of the compressor is 7 A.

7A COM­ PRESSOR HEATER

"

L2

Parallel circuit: A parallel circuit is a circuit ,vith paral­

lel paths for current flow as shown in Figure 1-13. The voltage is the same across each of the loads. Ho,vever, the current through each load varies. The figure shows a parallel circuit ,-vith four loads. The 110-V po,ver supply is applied across each load. The total a1nperage provided by the povver supply is equal to the co.mbined amper­ age in each of the branch loads. For example, the total amperage ,vould be 10 amps: ■ The amp draw of the light bulb is 1 A. ■ The an1p draw of the fan motor is 2 A. ■ The amp draw of the cornpressor is 7 A.

Amperage ■ Resistance.

■

Ammeter: An ammeter is an electrical instrument used

to 1neasure amperage. The ammeter can be part of a multimeter, as previously shovn1 in Figure 1-15, or it can be a stand-alone meter. One popular amperage meter uses a clamp device that opens around a ,v.ire to measure an1perage. Figure 1-16 shows a common clamp-on type of ammeter used in our industry. Current fl.o,v creates n1agnetism in the wire. The clamp-on meter converts 50 D.

Combination circuit: A combination circuit is a circuit

that con1bines series and parallel circuits, as illustrated in Figure 1-14. This is the most comn1on type of circuit found in HVACR equipment. Part of the circuit is in series with the load and part is in parallel ·with the series circuit. The R, and R2 resistors are in parallel \'\rith each other. This paral­ lel circuit is in series ,vith the R3 resistor. It is essential to understand the various types of circuits found in HVACR equip1nent. Identifying the type of circuit assists the tech­ nician in understanding and troubleshooting equipment.

230V

100 D,

100n R2

Voltmeter: A volt1neter is an electrical instnunent used

to measure voltage. The voltmeter is usually pa1·t of an electrical instrument called a multimeter. As the name in1plies, the multimeter in Figure 1-15 contains several electrical n1eters in one case. The n1eter should 1neasure: ■ ■

DC volts AC volts

L2 ____,.....____________.

Figure 1-14 This is a series-parallel or combination circuit. The R1 and R2 resistors are in parallel with each other. This parallel circuit is in series with the R3 resistor.

6

UNIT 1

that magnetic field into an amperage reading. The greater the current flo,.v, the greater the magnetic field developed by the wire and, hence, the higher the amperage. Ohmmeter: An ohmmeter is used to measure resistance in a load such as a motor or relay coil. The ohmmeter is usually part of a 1nulti1neter, as previously shown in Figure 1-15. VOLTS�-

-- RESISTANCE

1.4 COMBINING VOLTS, AMPS, AND RESISTANCE Figure 1-17 sho\VS a simple circuit that con1bines voltage, amperage (current), and resistance into one series circuit. This is a DC voltage circuit that pO\\'ers a resistor or simple heater. As you vvill soon learn, the electrical symbol for a re­ sistor and heater are the same. Pressure fro1n the DC voltage pushes electrons through the resistor. Figure 1-18 illustrates the Oh1n's la\\ formula, which v.rill be discussed in detail in Unit 2. Notice that the formula uses voltage, current, and resistance, which can be measured "vi.th a multimeter. Ohm's la,v can be used only ,.vith resistive circuits such as a resistor or heater. Electrical symbols: Electrical symbols are representa­ tive images of electric components in a ,,vi.ring diagram. Generally these sy1nbols do not look like the electrical 1

Figure 1-15 This multimeter includes options for measuring

voltage, resistance, and amperage. A voltmeter is usually part of a multimeter.

(V)VOLTAGE +

I

==n

(A)CURRENT

(!'l) RESISTANCE

Figure 1-17 A simple circuit that combines voltage, amperage

(current), and resistance into one series circuit. Pressure from the DC voltage pushes electrons through the resistor.

(V)

VOLTAGE

V=AxQ

WHERE: V=VOLTS A=CORRENT IN AMPS (A) (Q) CURRENT RESISTANCE Q = RESISTANCE IN OHlvIS

Figure 1-16 An ammeter is clamped on to a wire so amperage

can be measured.

Figure 1-18 Formula for Ohm's law. Ohm's law can be used

only with resistive circuits such as a resistor or heater.

WHAT YOU NEED TO KNOW TO UNDERSTAND ELECTRICITY

OPEN

S\VITCH

THERMOSTr\T

* CLOSED S\VITCH

Figure 1-19 Here are a few symbols that

---f

111-

BATTERY

components they represent. Symbols are like the images that are seen on road 1naps. Syn1bols are covered in detail in Unit 17. Figure 1-19 illustrates some common symbols used in heating, air conditioning, ventiJation, and refrig­ eration. See the back cover for a con1plete list of co1nn1on electrical symbols used in the HVACR industry. Electrical legend: An electrical legend i.s co1nparable to a legend found on a road map. The legend shovvs vvhat each symbol represents. A typical legend for an air conditioning condenser is sho•..vn in the acco1npanying table. The components are abbreviated because there is li1nited space on an electrical diagram for spelling out all of the component nan1es. For example, "CONT" is the abbreviation for the contactor. A contactor is an electromechanical sv.ritch used to provide power to the compressor and condenser fan motor. A list of abbre­ viations and acronyms is provided in Appendix A at the back of this book. There is no universal standard for legends or symbols, so you will find variations among manufacturers. Wiring Diagram Legend for an Air Conditioning Condenser

CAP CH CHS COMP CONT CTD DTS HPS IFR

LLS

LPS OFM OPS SC SR ST

7

Dual-Run Capacitor Crankcase Heater Crankcase rleater S·witch Compressor Contactor Compressor Time Delay Discharge Temperature S,vitch High-Pressure Switch Indoor Fan Relay Liquid Line Solenoid Valve Lo,v-Pressure S,\ritch Outdoor Fan Motor Oil Pressure Safety Start Capacitor Start Relay Start Thennistor

Wiring diagram: A \'vi ring diagran1 or schematic is the road map of the electrical system. Figure 1-20 shows a

typical ,-viring diagran1 \\'ith symbols and ,-viring connec­ tions for a residential condensing unit. Such diagrams help technicians find their way around a circuit. It is an aid for troubleshooting the systen1. Various types of ,vir­ ing diagrams are discussed in detail in later units.

�

FUSE

may be used in understanding an electrical diagram. The symbols are joined to form an electrical diagram, which is like a road map for the HVACR system. See the back cover for a complete list of common electrical symbols used in our profession.

Circuit boards: As our kno\\'ledge of electronics has

advanced, additional circuit boards are being used in air conditioning and heating equipment. See Figure 1-21. Circuit boards, sometimes called solid-state circuit boards, are used to reduce and 1niniaturize the number of components in HVACR equipment. The term solid state means that the components are not 1nechanical and do not have moving parts. Some circuit boards have microprocessor circuits that assist in troubleshooting the equipment. This topic will be discussed in Unit 19.

TECH TIP Keep an open mind! Electrical troubleshooting requires experience and an open mind. Troubleshooting means that you are going to find the problem and repair it. At first you will need help. Experience comes with time and working on the job doing various HVACR activities. Even working around properly functioning equipment and cleaning equipment provide valuable experience. It is important to know how a system is supposed to oper­ ate when everything is functioning correctly. Keeping an open mind is most important until the new technician gains experience. Being open minded means checking all options and exploring the unknown. Many times in our profession we will not totally under­ stand every piece of equipment that we have to trouble­ shoot. The technician must be able to determine what is working in order to troubleshoot what is not working. This is done by carefully checking and eliminating sec­ tions that are not creating the problem.

SERVICE TICKET Using electrical terminology correctly is important when you communicate with and get assistance from your supervisor. Let's use the following example to see why. As an air conditioning apprentice, you are sent to survey a problem with a small commercial refrigera­ tion job. The customer says the cooler is getting warm and the outdoor section is not operating. You recently purchased and learned to operate some of the basic electrical instruments such as the voltmeter and clamp­ on ammeter. You are not expected to do the final trou­ bleshooting, but to report back to the office with an initial finding since the experienced technician will soon

WHAT YOU NEED TO KNOW TO UNDERSTAND ELECTRICITY

9

communicate with your supervisor, the manufacturer's tech support people, and customers. These tenns \vill be discussed and applied in more detail in the following units. Some of these tenns are easily misunderstood or confusing. You sa'¼' in the Service Ticket scenario that using the ,,vrong tenn can change the outcome ,vhen communicating with a supervisor or other technician. Yes, there are 1nany ne,,v terms to learn and understand. Refer back to these tenns or the tenns in the glossary at the end of the book to drill do-wn to the funda­ mental terms needed to become a good technician.

REVIEW QUESTIONS 1. \-Vhat is electricity?

Figure 1-21 Several types of circuit boards are found in air conditioning units.

2. vVhat is current flow or an1perage?

3. What creates a magnetic field in a conductor: voltage or current flow? 4. vVhat is voltage? 5. What is the difference between a conductor and an insulator?

follow. This is a chance to show the company the "new tech" knows a little something. You notice that the condensing unit is not working. The evaporator blower is operating. You decide to do a few checks on the condensing unit. The voltage meas­ urement at the disconnect and the condenser is 120 volts. The disconnect is the power switch. You decide to call the office with this information and seek advice on how to proceed. You talk with a supervisor and state that you measured 120 amps on the condensing unit. The supervisor repeats in a loud voice, "120 amps!" The supervisor tells you that the compressor might be locked up or there could be a problem with the starting components on the compressor and gives you a few tips on what to check. The compressor is not the problem. unfortunately, you reported the 120-volt measurement as 120 amps, which changed the way the system was approached for troubleshooting. Knowing the correct terminology is important to save time troubleshooting and prevent embarrassment.

SUMMARY This unit was an introductory section that introduces some basic terms used \Vhen working \Vith HVACR equipment. It is essential to understand these basic terms in order to

6. vVhat are the two common types of electricity? 7. What is control voltage? 8. Vv'hat is resistance?

9. vVhat is a watt?

10. How are watts calculated? 11. vVhat is a 1neant by a load?

12. vVhat are the differences an1ong a complete circuit, an open circuit, and a short circuit? 13. vVhat is a series circuit? 14. vVhat is a paraUel circuit? 15. What is a combination circuit? 16. vVhat is the 1nost common equipment?

type

of circuit found in HVACR

17. What is an electrical legend? 18. Looking at a diagram legend, what does LPSmean? Vv'hat does HPSmean?

19. How are optional components marked in Figure 1-20? 20. vVhy are circuit boards used in HVACR equipn1ent?

UNIT 2

Ohm's Law and Circuit Operation WHAT YOU NEED TO KNOW After studying this unit, you will be able to: 1. Calculate volts, amperage draw, and resistance using Ohm's law. 2. Identify series circuits. 3. Apply the series circuit laws to electrical circuits. 4. Identify parallel circuits. s. Apply the parallel circuit laws to electrical circuits. 6. Identify combination circuits. 7. Calculate volts, amperage draw, and resistance using the watts formula.

Learning hov\T to use Ohm's la\11 ,.vill help you understand ho,.v current and voltage flow in a circuit. In this unit vve discuss how resistance affects circuit operation. Resistance changes the current flo,,v and has an influence on the volt­ age drops in a circuit. We ,vill see that voltage, current, and resistance have an influence on each other. First, 'Ne revie,,v the types of circuits. They are:

Finally, Ohm's law and the watts formula are only ac­ curate with resistive loads. Resistive loads are electric heat­ ers, crankcase heaters, resistors, or incandescent bulbs. The other types of loads, inductive or capacitive loads, use a more complex formula to detern1ine current and voltage conditions. The resi.stance in an inductive or capacitive cir­ cuit is called impedance. The impedance formula includes resistance plus the effects of 1nagnetism or capacitance. Inductive loads are devices that use magnetism to operate a component. For example, a motor, transforn1er, or relay coil is an inductive load. An inductive load in the form of a 1notor and trans­ former is shown in Figures 2-lA and 2-lB, respectively. A capacitive load has a capacitor in the circuit. A dual­ run capacitor is sho'¼'n in Figure 2-2. The resistance the ca­ pacitor creates is called capacitive reactance. Many loads have a co1nbination of resistance, induction, and capacitance. These loads will be discussed throughout the book, but learn­ ing the impedance forn1ula is beyond the scope of this book and really not necessary to do troubleshooting. Learning and understanding Ohm's la'¼' and the '¼'atts forn1ula, ho,vever, vvill aid in the troubleshooting process.

■ Series circuits ■ Parallel circuits ■ Combination circuits.

These circuits were discussed in Unit 1. The discussion here v\Till be more detailed. It is important to understand these circuits to solve Ohm's law problems, but 1nore in1portantly to learn ho,,v current and voltage flow vary in a circuit. This concept is fundan1ental to troubleshooting. The technician has to understand the relationship of volt­ age, current, and resistance to be able to troubleshoot. The relationship is knovvn as Ohn1's lavv. If you do not learn this concept, you ,vill not be able to troubleshoot HVACR equipment beyond the obvious burned-out co1nponent, ·which is just a small part of the overall troubleshooting process. This unit shovvs you how to solve Ohm's law and, 1nore importantly, ho\v to use it to understand circuits and troubleshooting. This unit also explores the use of the watts formula. So1ne calJ. it Watt's la,v, but that is incorrect. It is a variati.on of the formula for Ohm's la,v. The vvatts formula compares the voltage and current fl.o,,v in a circuit to detern1ine how it affects the co1nponent vvattage. The v,ratts formula is also referred to as the power formula or power calculation. 10

Figure 2-1A A motor worl r m r m (") -l ;o (") )> r (") 0 0 m

'°.......

98

UNIT 6

SERVICE TICKET The second service call of the day is a poor cooling complaint. You arrive on the job around 10 a.m.; the customer confirms that the cooling system does not cool well when the temperature rises during the day. The cus­ tomer states that the cooling seems to "come and go." He says, "The air from the ductwork is continuous, but sometimes it is warm and sometimes it is cold. The sys­ tem cools well later in the evening and in the morning." You start the logical troubleshooting process (ACD of checking the airflow from the ductwork. The airflow is cold and seems to be flowing at a good velocity. The air filter is clean. The thermostat is set to cooling and the temperature is low enough to keep the house comforta­ ble. The temperature is lowered so that it does not cut off while troubleshooting. The indoor temperature is 75 ° F and the outdoor temperature is 85° F. The condenser is rejecting heat as indicated by the warm air felt coming from the top of the condenser. The liquid line is warm and the suction line is cold. The manifold gauge set is hooked up. The pressures are good. The amperage to the common wire on the compressor is 18 amps. The name­ plate on the condenser shows the rated load current to be 19 amps. You check the superheat and subcooling and they are surprisingly perfect. What is the problem? The amperage draw is a little high. You do not ex­ pect the amperage to be this close to the nameplate am­ perage unless the outdoor temperature is much higher. You verify the amp reading with a second clamp-on am­ meter. The second ammeter reads 18.2 amps. The input voltage and control voltage are good. The voltage drop from the panel to the unit is around 2%. The equipment has been operating for 25 minutes without shutting off. The indoor temperature is dropping. You stop the system and check the running com­ ponents. The contactor contacts and run capacitor are good. All wire connections are fairly tight. One wire on the contactor is loose and you tighten it. When tightening the wiring you notice that the white conductor coming from the disconnect to the contactor is darkened. This could be an indication of overheating. After obtaining permission from the customer, you change the wire. The wire from the disconnect is 12 AWG, which is good for 20 A. The nameplate on the condensing unit requires a 30 ampacity conductor. The 30 ampacity rating will cover 125% of the compressor motor amps plus the condenser fan motor amperage, which is usually a few amps. You decide to change the conductors to 1o AWG, ° 90 C, THHN wire. After the condensing unit is restarted, the compressor amperage drops to 16.8 A. Replacing the disconnect conductor and tightening all connections drops the amp draw by about 12%. This might be the solution to the problem. After showing the customer the overheated wire, you tell him that the wire needed replacing and explain

what was done and why. You notify the customer that the equipment did not fail when it was being serviced and tell him to contact you immediately if he has any further problems. The invoice is completed and signed by the customer. You collect the agreed-on fee and pro­ ceed to the next service call. Note: An intermittent problem is one of the big chal­ lenges faced by a technician and the customer. Unless the problem occurs while the technician is on the job, an attempt at a solution may not truly solve the problem. If this is the case, the customer may become impatient. Be sure to let the customer know what steps were taken and that the problem may not have been solved. Assure the customer you did the obvious, but to immediately call your office if the problem reoccurs. Show the cus­ tomer the phone number on the invoice.

SUMMARY The purpose of this unit w·as to familiarize you with the National Electrical Code and hovv it impacts our profession. The NEC is a safety code that covers electrical installations and electrical components. It is in1portant to understand that although HVACR has a code called the Uniform Mechanical Code, we must also follow all building, plumbing, electrical, and life safety codes. This unit discussed several electrical requirements that must be considered ,,vhen installing HVACR equipn1ent. For example: ■ ■

■ ■

Required disconnects (unless the breaker can is nearby and can be seen by the technician) \Vire sizing Use of nameplate data to size \-vire and breakers Electrical requirements directed by the NEC.

All HVACR equipment shall have a positive n1eans of removing or disconnecting pO\-ver. The electrical disconnect is generally sized to handle 125% of the rated load a1nperage. General ,-viring in commercial and industrial buildings shall be protected inside conduit. Open wiring, n1eaning wir­ ing not inside conduit, is allo,,ved inside residential installa­ tions. Even if not required in many residential installations, it is a good idea to have all conductors in conduit ,-vhen pass­ ing through supply or return air ducts. Conductor insulation burning inside a duct can quickly distribute smoke through­ out a structure. NEC Table 310.15(B)(l6) is one of the 1nost important sections in the NEC. Table 310.15(B)(l6) is used by techni­ cians to determine the correct ,-vire size based on conductor type (copper or alu1ninum) and application temperature. If a wire burns open or overheats, the ,-vire table should be consulted. Burned or overheated \-Vires are not always caused by undersized conductors. This condition can also be caused by loose connections or a load that is partially shorted. An

NATIONAL ELECTRICAL CODE® asterisk(*) on wire sizes in NEC Table 310.15(B)(l6) means that the maximum wire size should be reduced by 5 A. This exception affects wire sizes AvVG 14, 12, and 10. We learned that there is important infonnation on wire insulation. The cover or jacket of the w'ire shO'ws the AWG vvire size, and the letters on the insulation indicate the fea­ tures of the insulation coating. THHN and THvVN wire insulation is co1n1nonly used ,-vhen hooking up HVACR equipment. Understanding and using the NEC is extremely i1nportant for the advanced technician.

REVIEW QUESTIONS

99

7. What copper wire size is selected for a condensing unit that requires 35 ampacity at 90 °C? 8. v\That aluminum wire size is selected for a condensing unit that requires 35 ampacity at 75°C ? 9. 1'1ost wire discussed in this unit has what maximu1n voltage rating? IO. vVhat are the two in1portant ratings found on fuses?

11. Use Table 6-7 to answer this question: \Vhat wire size is required when installing heater model BAYHTRNl0SA; unit model WCCO18Fl? State wire type, te1nperature, and gauge.

12. Use Table 6-7 to answer this question: \Vhat wire size is re­ quired when installing heater model BAYHTRN105A; unit 1nodel VvCCO42Fl? State wire type, temperature, and gauge.

1. What are two ways to locate infonnation in the NEC? 2. vVhat is the purpose of a disconnect on a piece of HVACR equipment?

3. The rated load pov.rer requirement of a condensing unit is 100 A. \Vhat size circuit breaker is needed? 4. Where is open wiring or wire not protected by conduit allowed?

5. \Vhat three conditions create high resistance in wire conductors? 6. What copper wire size is selected for an air handler that re­

quires 10 ampacity at 9°C?

13. Use Tabl.e 6-8 to answer this question: \,Vhat happens to the

Btuh heat output when co1nparing operations at 208 and 240V? 14. Use Table 6-8 to answer this question: \-\That is the breaker size and wire size for strip heater n1odel #BAYHTRl 1.7A? State the wire type, insulation, and ternperature rating. IS. Using the nameplate shown in Figure 6-28, what four pieces of information on the nameplate are required by the NEC?

16. Using the nan1eplate shown in Figure 6-28, what is the LRA?

Table 6-7 Table for Review Questions 11 and 12

-

-

Single Circuit Power Ampacity and over current Protection Single Power Entry Kit

--

Heater Model

BAYHTRN105A

BAYHTRN108A BAYHTRN310A BAYSPEK047A

BAYHTRN310F

BAYHTRN410A BAYHTRN41OF

BAYHTRN415A

BAYHTRN420A BAYHTRN430A

(Courtesy Trane Corporation.)

-

Unit Model

-

Max Min overCKT Current AMP Device '-

WCCO18F1

44

45

WCCO24F1

45

50

WCCO30F1

52

60

WCCO36F1

52

60

WCCO42F1

58

60

WCCO18F1

57

60

WCCO24F1

58

60

WCCO36F3

50

WCCO42F3

-

Single Power Entry Kit

-

Heater Model

'"

Unit Model

Max Min overCKT Current AMP Device

WCCO30F 1

113

125

WCCO35F 1

116

125

WCCO42F 1

122

125

WCCO48F 1

126

150

WCCO48F 1

156

175

WCCO30F 1

63

70

WCCO36F 1

66

70

50

WCCO42F 1

72

80

54

60

WCCO24F 1

70

80

WCCO48F3

59

60

WCCO30F 1

76

80

WCCO36F4

26

30

WCCO36F 1

78

80

WCCO48F4

29

30

WCCO42F1

84

90

WCCO60F4

32

35

WCCO48F1

89

100

WCCO36F4

33

35

WCCO24F1

78

80

WCCO48F4

37

40

WCCO30F1

83

90

WCCO60F4

39

40

WCCO36F1

86

90

WCCO48F4

44

45

WCCO42F1

92

100

WCCO60F4

46

50

WCCO48F1

96

100

WCCO60F4

61

60

WCCO60F3

122

125

BAYSPEK048A* 1

BAYHTRN117A /

BAYHTRN123A BAYHTRN108A

BA YHTRN110A BAYSPEK049A*

BAYHTRN112A

BAYSPEK050A*

BAYHTRN330A

100

UNIT 6 Table 6-8 Table for Review Questions 13 and 14 Single-package cooling and heat pump systems without single-power entry kits will normally have two branch circuit power supplies if electric heaters are included: one branch circuit to serve the single-package system and one to serve the electric heater.

Heater Model BAYHTRN105A BAYHTRN108A BAYHTRN110A BAYHTRN112A BAYHTRN115A BAYHTRN117A NONE

.

Volts 208 240 208 240 208 240 208 240 208 240 208 240

AMP 18 21 28 32 36 42 42 48 54 62 62 72

KW

3.74 4.98

5.76 7.68 7.47 9.96 8.64 11.52 11.21 14.94 12.97 17.28

Max. Fuse or HACR CKT BKR Size 25 30

MCA 22 26

35 40 45 52 52 60 67 78 C/8 90

--

35 40 45 60 60 60 70 80 8U 90

(Courtesy Trane corporation.)

T-y1> '"I1 c:::::a tv '"I1 11::J N '1111::J N 'I] t:::a N � c:::::a tv .,, 11::J '.;J .,, 11::J ,..,, .,, 11::J t.,l .,, 11::J :.,:, .,, c:::::a w .,, c:::::a (.,.) .,, c:::::a ,..,, c:::::a ,..,,

060, 3.5T080

DEF.

5252

700

875

1050,

I�25

1225

1225

5T080, 100

DEF.

7002

875

1050

1225

17501

1750

---

---

lL)0

• I\--

(. 1400)

1750 1

2100

. '- 120

----· ·

.....

••

r «•.!,

.. ---..

.........

BASED ON 400 CF.MfION (SETUP SWITCH S\Vl-5 ON) .MODEL SIZE

SETUP SWITCH SW3 POSITIONS 11::J - 0 c:::::a - 0 11::J � 0 c:::::a ...... () a::::J "'"""' 0 c:::::a ,..... C a::::J"'"""' 0 c:::::a 0 11::J Iv 'T1 II::] N 'T1 t:::a N 'Tl t:::a N 'T1 11::J N 'Tl 11::J N '"ti t:::a N '"ti t:::a N c:::::a ..,., '11 t:::a (.;l 'T1 c:::::a (>.) '"r1 c:::::a w 'I1 11::J (>.) '"r1 11::J ,__, '"I1 11::J w 'I111::J w

:a

060, 3.5T080

DEF.

6002

800

1000

1200 1

1400

1.400

1400

5T080, 100

DEF.

8002

IOOO

1200

1400

1600

20001

2000

120

DEF.

800

10002

1200

1400

1600

20001

2100

l. DEFAULT A/C AIRFLO\V \VB.EN A/C swrrcHES ,-\RE IN OFF POSITION 2. DEFAULT CONT. FAN AJRFLO\.VVv'HEN CF S\VITCHES ARE fN OFFPOSTTION 3. S\VITCHPOSITIONS ARE ALSO SHO\.VN ON FURNACE Vv1RING DIAGRAJvl (Courtesy carrier Corporation.)

ELECTRICAL INSTALLATION OF HVACR

----

l

-

111

REMOTE AIR-COOLED CO DENSER

Tl IREE-PHASE/60 HZ POWER SUPPLY

l

DISCONNECTS

CHILLED LIQUID REFRIGERA T POWER WIRI G CO TROL WIRI G

Figure 7-16 This chilled water system has four electrical circuits feeding four different parts of the system.

The blov.,er dip sv.ritches should be set for the partjcular ap­ plication, v.1hich is usually different than the factory default setting. For example, in hot and humid climates, the blo,ver speed should be set for 350 CFM per ton, not 400 CFM per ton. The lo,ver speed -.vill allo,v more air contact tin1e ·with the evaporator, thus removing a greater amount of moisture from the air. Using Table 7-1, you ,�rould select the dip sv.,itch setting for 350 CFM/ton for model size 120 for a 4-ton condensing unit. This is a good switch selection for ,varm and humid clilnates. This ,vill be 350 CFM X 4 tons = 1400 CFM. 1n the upper section of Table 7-1 locate model size 120 and set for 350 CFM per ton. Go to the right of the table until 1400 is located. Go up the top of the table to see the selected dip s,.vitch settings. The dip s,vitch settings are the \\7hite, rec­ tangular boxes. The dip switch is a white plastic slide s,vitch as previously shown in Figure 7-15. Here are the required dip switch settings for this exa1nple: S,-vitch 1 ,vill be in the on position. S,v.itch 2 vvill be in the off position. S-.vitch 3 -.vill be in the on position These dip s,vitch settings \-vill ensure that the 4-ton blo,-ver ,-vill develop 1400 CFM or 350 CFM/ton. This is good setting for hot and humid climates.

7.5 LARGE HVACR SYSTEMS Large HVACR systems have multiple electrical requirements. Each piece of equipment n1ay have a different ,,vire size require­ ment because they probably use different voltages and have dif­ ferent amperage needs. Each piece of equipment has a different disconnect, as required by the NEC. The disconnect should be \.Vi thin line of sight of the equip1nent it services. In some cases, a breaker panel can be the disconnect if it is near the equipment it serves. Older installations ,vere not required to have a separate disconnect; therefore, you ,-vill find 1nany older systems \\Tith no disconnect. A disconnect ,-vill be installed ,,vhen the equipment is replaced, because code updates are required when changing out n1ajor components of a systen1. Figure 7-16 is an example of a chilled water systen1 that has four circuits feeding four different parts of the system. Four dis­ connects 1nust be sized for the piece of equipment that is hooked to the po,ver source. The a1np dra,,v of the piece of equipment vvill determine the size of the disconnect. In this figure the dis­ connects are ,,vired to the follov.,ing systen1 components: ■ • ■ ■

Chiller co1npressor motor Re1note air-cooled condenser Liquid chiller pump Air handling unit.

112

UNIT?

Figure 7-17 A large disconnect is

found on high-tonnage equipment. The disconnect is mounted on the brick wall. The smaller disconnect, located below the main disconnect, is used to feed power to a supplemental control in the chiller. The compressor inset is shown to emphasize the largest current drawing device in this large package chiller unit.

Figure 7-17 illustrates the large disconnect found on high-tonnage equipn1ent. The disconnect is located on the brick wall to the right of the chiller. Note that there is another sn1all disconnect belo,-v it. The fan grilles, as seen on the top of the unit, indicate that it is an air-cooled systen1.

case. Figure 7-18 sho\.vs a green bonding wire. Green wire indicates a ground.

7 .6 ADDITIONAL ELECTRICAL REQUIREMENTS In addition to having the correct conductors supplied to the HVACR equipn1ent, there are other electrical requirements per the Uniform Mechanical Code (UMC) and National Electrical Code (NEC). Some of these code requiren1ents make the ·work environment easier on the technician, \.Vhile other requirements make it a safer working area. Let's review son1e of these requirements.

..--GROUND

WIRE

(GREEN)

Bonding Jumper A bonding jumper is a ,vire that connects all of the equip­ ment to a ground rod. According to the NFPA and NEC, the bonding jumper is a reliable conductor to ensure re­ quired electrical conductivity bet,�1een the 1netal casings of equipn1ent. If the continuity is broken, the equipment can become a dangerous shock hazard if a hot wire touches the

Figure 7-18 A bonding jumper is a wire that connects all of

the equipment to a ground rod.

ELECTRICAL INSTALLATION OF HVACR

113

100

SAFETY TIP It takes less than an amp to kill you. Figure 7-19 illus­ trates the effects of current on the human body. A poor or broken ground can kill you. If you ground yourself while touching equipment that has a short, you will be­ come the bonding jumper or ground.

90 80 POSSIBILITY OF DEATH

70

Permanent Lighting According to the NFPA, pennanent lighting shall be provided in attic and basement areas near the equipment. Permanent lighting shall be provided at the roof access for roof-top units. The light switch shall be located inside the building near the attic, basement entrance, or roof access. Figure 7-20 sho,.vs an installation's light s,vitch and light arrange1nent. The s'vvitch is in the attic near the entrance.

SEVERE PAIN AND UNCONTROLLABLE l\tlUSCULAR CONTRACTIONS ----AND BREATHING DIFFICULTIES THRESHOLD OF UNCONTROLLABLE PAIN

30

20

PAIN

10

Protection The Uniform Mechanical Code requires that H\fACR appli­ ances be protected against damage in garages, ,,varehouses, or other areas subject to mechanical dan1age. The specific type of protection is not stated. in the code. The UMC does specify

1

THRESHOLD OF �-""-- FEELING CURRENT

Figure 7-19 Amperage rating of electric current creating

various shock effects from 1 to 100 mA. It takes less than an amp to kill you.

VENTILATED ATTIC SPACE

RECEPTICAL LIGHT S\VlTCH

(

� 8 �

--

I•

--

•: = = = = = = � � � •-•---+·-----

30" x 30" MI- N MU_ i - lM_•· l : ACCESS I,! OPENING !LS

PERt.1ANENT ELECTRIC LIGHT

SUPPLY AIR

EQUIPMENT DISCONNECT 20' �IAXI:tvJUM

�

I

-0

PIPE

='®i .:= =-=- --

6' - 6"

�1TNIMUM ------. HEIGHT 1 1 ,--�'�--------+i.......1

�I]

�---''I

FURNACE AND COOLING UNIT MOUNTED IN ATTIC

t

RETURN .A:IR

Figure 7-20 Permanent lighting and light switch placed according to NFPA requirements. This drawing also shows other access requirements

for an attic installation such as a 30-in. x 30-in. access and a distance of no more than 20 feet from the access point to the equipment.

114

UNIT?

Figure 7-21 A disconnect is required on a condensing unit unless it is within line of sight of an electric panel box.

Figure 7-23 This is a clean attic installation of an air conditioning evaporator with a gas furnace. The disconnect for the furnace is a simple light switch.

that heating and cooling equipment located in a garage shall be installed at least 18 in. above the floor level.

not re1nove control voltage. Control voltage po,,ver is usually controlled fron1 another, indoor source. The gas furnace in Figure 7-23 has a light S\Vitch style of disconnect. A 120-V receptacle shall be located ,vitbin 25 feet of the equipment for service and maintenance. According to the Ul\.1C the receptacle does not need to be located on the same level as the equipment. This staten1ent leads to code interpretation issues. For example, son1e code jurisdictions allow 25-foot access to a receptacle even if the po,,ver for an extension cord has to go through an operable ,vindow. Other code interpretations consider the outside or the attic or basen1ent as the same area. They don't consider access through ,,vindo\vs, doors, or ,,valls to po\,,er as acceptable. In other ,,vords they ,vould require a 120-V receptacle near the outdoor equipment. Again, check ,-vith the local inspector or code jurisdiction before 1naking any equip1nent change-outs. Changing out equip­ ment may require a code update, "vhich means lighting and access to 120-V po,,ver as ,-vell as other code-required upgrades. Lo\v-voltage wiring (50 volts or less) should be in­ stalled to prevent physical damage to the conductors. ln most installations this does not require conduit inside or outside the building. Best practices dictate that outside low­ voltage \viring be protected in some form of conduit or pip­ ing outside the building. Some homeowners' associations do not allo\V open \viring, \Vhich means it must be enclosed in conduit.

Electrical connections Electrical disconnects should be ,vithin sight of the equip­ ment. Equipment \vith more than 50 volts shall have a dis­ connect. A "pull-type" condensing unit disconnect is show·n in Figure 7-21. Figure 7-22 is a close-up vie\'\' of the condens­ ing lu1it disconnect. When the disconnect is pulled, there is no high-voltage po\'\1er to the condenser. The 24-V control voltage n1ay still be present at the unit. This disconnect does

SAFETY TIP Figure 7-22 This pull disconnect for a condensing unit is rated for 60 A, which will more than handle the total load of the condenser, which is 25 A. The "pull" is sitting on the top of the disconnect, ensuring that no power is supplied to the condensing unit.

Combustibles within commercial supply or return air ple­ num ducts are not allowed. Combustibles create flame spread and smoke development. combustibles include

ELECTRICAL INSTALLATION OF HVACR

115

Model 2AC14*"'18P. The voltage, hertz, and phase column is next. This 111odel uses 208-230 volts at 60 hertz and is single phase. The 208-230 volts is allo,-ved a :±: 10% variance belo,v 208 volts and above 230 volts. The + 10% voltage range is calculated in the next colu1nn as 197-253 volts. The minimum circuit ampacity is 9.7 A, which n1eans the wire size should handle 10 an1ps. The 1naximum overcurrent de­ vice for this model number is listed as 15 a1nps. The fuse or circuit breaker should be no larger than 15 amps, so the con1pressor RLA should dra,v no n1ore than 6.9 a1nps. The LRA or starting amps is 35 A. The fan motor FLA is 1.1 A, at l/ 10 horsepo,-ver at 1,075 RPM. The refrigerant charge is 1.06 ounces, and the condenser ,veighs 185 pounds. Other important installation notes are listed at the botton1 of the table.

standard electrical conductors that are not in conduit, thermostat wiring, and most communication cables. Plenum-rated cable or fire-rated cable can be pur­ chased and used in these air ducts. The insulation sheath on the insulation of plenum-rated wire meets the code requirements and is safe for this type of in­ stallation. Ducts serving residential structures are ex­ empt from the "no combustibles in the air duct" code requirements. some residential ducts even have wood or drywall in the return air duct as well as unrated thermostat wiring. To be clear, commercial and industrial wiring is re­ quired to be in conduit inside or outside the ductwork. In most residential installations the wire does not need to be in conduit unless it is exposed outside the structure. For example, Romex can be run in residential attic spaces or between walls and under floors. Outside residential wiring will need conduit protection.

7.8 INSTALLATION NOTES Most installation instructions have a section called Notes. Revie\V the notes under Table 7-2. This is additional infor­ mation that n1ust be follo,ved to ensure the safety and de­ sign performance of the installation. This information is not intended to be all encompassing, but gives an idea of the important subjects covered in this often overlooked section. Here is an excerpt from one manufacturer's notes found in a natural gas furnace installation Notes box:

7.7 INSTALLATION INFORMATION Table 7-2 shows electrical and physical data that is valuable when doing a ne,-v installation or a condenser change-out. Let's revie,-v some of the information so that you ·will understand its value. On the left side of the table, start ,-vith

I. If any original wire is replaced, use ,vire rated for 105°C.

Table 7-2 Electrical and Physical Data for various condensers This table gives the installing technician electrical information about various condensing unit model numbers.

Model

Voltage/HZ/ Phase

Maximum Compressor over Min. Current Rated Locked Device Load Rotor Voltage Circuit (Amps) (Amps) Range (amps) Amp.

Weight (lbs.)

Fan Motor Full Load Amps

Refrig. Rated Norn. Charge HP RPM (OZ.r

2AC14**18P 208-230/60/1 197-253

9.7

15

6.9

35

1.1

1/10

1075

106

2AC14**24P 208-230/60/1 197-253

11.6

20

8.4

39

1.1

1/10

1075

129

2AC14**30P 208-230/60/1 197-253

15.2

25

11.3

51

1.1

1/5

1075

154

2AC14**36P 208-230/60/1 197-253

17,2

30

12.9

61

1.1

1/5

1075

165

2AC14*42P

208-230/60/1 197-253

21.5

35

16.2

82

1.2

1/4

1075

204

2AC14*48P

208-230/60/1 197-253

22.6

35

17.1

100

1.2

1/4

1075

208

2AC14*60P

208-230/60/1 197-253

28.8

50

21.4

137

2.0

1/3

1075

264

Do Locate the Unit:

• With proper clearances on sides and top unit (a minimum of 12" on the three sides. service side should be 24" and 48" on top • On a solid, level foundation or pad • To minimize refrigerant line lengths (Courtesy Allied Air Enterprises.)

-

-

Do not Locate the Unit:

• • • • • •

Wire Guard/ Louvered 185 -

201 227 226

-

262 261

270

on brick, concrete blocks or unstable surfaces Near clothes dryer exhaust vents Near sleeping area or near windows Under eaves where water snow or ice can fall directly on the unit With clearance less than 2 ft. from a second unit With clearance less than 4 ft. on top of unit

J I

7

116

UNIT?

Table 7-3 Required Field-Installed Accessories for Air Conditioners

This table lists various installation requirements. Required for Low-Ambient cooling Applications {Below 55 ° F/12.8 ° C)

Accessory

Yes Yes Yes (For non-Infinity systems only)

Crankcase heater Compressor start assist capacitor and relay Evaporator freeze thermostat

No

Liquid line solenoid valve Low-ambient pressure switch Support feet Thermal expansion valve (TXV) hard shutoff Winter start control

Required for Long Line Applications* {Over so ft. 24.38 m)

Yes Yes

No

see long-line application guideline

yes (For non-Infinity system only) Recommended Yes Yes (For non-Infinity systems only)

No

No

Yes

No

* For tubing line sets between 80 and 200 ft. (24.38 and 60.96 m) and/or 20 ft. (6.09 m) vertical differential, refer to Residential Split-System Longline Application Guideline. (Courtesy carrier Corporation.)

2. Only use copper ,-vire ben-veen the disconnect box and furnace connections. 3. Symbols are electrical representations only. 4. Replace circuit board fuse with a 3-amp fuse. 5. Blovver off delay, gas heating selections are 90, 120, 150 and 180 seconds, cooling or heat pu1np 90 seconds or 5 seconds vvhen dehumidifying call is active. Table 7-3 sbo,vs information about accessories that ·wi11 be valuable ·when evaluating the electrical and mechanical parts of the condenser. A condensing unit has several electri­ cal components. Figure 7-24 gives the technician more information that relates to the crankcase heater listed in the accessories table, Table 7-3. This crankcase heater is controlled by the dis­ charge line temperature. When the discharge line is ,varm, the crankcase heater ,-vill open the po,ver supply to the heater. The crankcase heater does not need to be operated when the

BLK

))

TE.MPSWLTCH

CRANKCASE HTR

BLK

con1pressor is running. This will save a little energy and ex­ tend the life of the heater. This could be considered a "green . . since . circuit 1t. saves energy. Figure 7-25 sho,vs an insertion-type crankcase heater, ,vhich you might find on a sen1i-hennetic compressor. The heater keeps the compressor oil warm during the off cycle to prevent refrigerant from condensing and diluting the lu­ brication. Figure 7-26 illustrates the location of a liquid line so­ lenoid valve, which is an option for the condenser model number found in Table 7-3. When the solenoid closes, the

BLK

BLK

Figure 7-24 The crankcase heater is not on all the time. When

the temperature drops the thermostat closes and operates the heater. This could be considered a "green circuit" since it saves energy.

Figure 7-25 This crankcase heater is installed in the crankcase

well. It is used to keep the oil warm to prevent refrigerant from condensing in the compressor oil.

ELECTRICAL INSTALLATION OF HVACR

117

Check operation of all pressure S\.vitches by creating a lo,-v- or high-pressure condition to cut off the equipment. ■ Operate the thennostat in all modes: heating, cooling, fan auto, fan on, and fan off. Check emergency heat with a heat pump system. ■ Program the thermostat per custo1ner's recommen­ dations. • Show the customer how to operate the thermostat. ■ Give the owner the thermostat and equipment owner's manual. ■ Record voltage, amperage, pressure, and charging in­ fonnation in a database to be used as a future service record.

■

SOLENOID VALVE

Figure 7-26 A system that includes a liquid line solenoid valve,

which is usually located near the air handler or metering device.

7.10 REWIRING EQUIPMENT compressor continues to operate, pumping down the system until it is shut do,-vn by opening the lov.r-pressure switch. This design removes refrigerant from the evaporator and suction line v.1hen there is a long refrigerant line set. Removing 1nost of the refrigerant will prevent co1npressor flooding. The so­ lenoid is usually installed near the air handler or metering device for the best design and operation.

SAFETY TIP When stranded wire (sometimes called braided wire) is used, a single strand of wire may separate and create a hazard. Wire should be inspected to ensure no strand of wire is loose. The loose wire may ground or develop a short circuit to a wire of a different potential. Stranded wire should be hooked around a screw or all conduc­ tors slipped into the electrical connector and crimped, then connected. one way to prevent a stray wire is to solder the stranded wires together or place them inside a wire ferrule. A wire ferrule is a small metal tube. The stranded wire is slipped into the ferrule and the ferrule is crimped closed. The ferrule is slipped under a con­ nection point and tightened. This will also improve the overall circuit conductivity at that connection.

7. 9 ELECTRICAL CHECKLIST This electrical checklist is used as a final punch list before turning over the operation of the equipment to the owner. You ""ill notice that it does not include any of the other im­ portant aspects of an installation such as airflow, ductv.1ork, and charging. A separate checklist should be developed for those critical items. Tighten all field and factory connections. ■ Check incon1ing voltage prior to starting equipment. ■ Start equipment. Record voltage and current readings \.vhile adjusting the charge. ■

In some cases a piece of equipment •..viii need to be rewired. A piece of equipn1ent can be analyzed and repaired if the tech has a ,-viring diagram and the ,-viring is still intact fronl the factory. When equipment ·wiring is modified \.Vithout docu­ menting the changes on a ,-viring diagram, the technician ""ill have trouble. One indication that wiring 1nodifications have occurred is ,vhen the tech opens a panel door and a bundle of ,vire falls out. Another is the sight of spliced \.Vire and ad­ ditional components inside the cabinet. The solution is not easy, but it is possible to solve the problem. The ans\.ver is to re1nove all of the ,viring and re\.vire the entire piece of equipn1ent. Use the original \.Viring diagran1 or one that is co1npatible ,-vith the unit that is being re,,vired. Wiring up the total unit and energizing it will not make it easy to find a problem quickly. Instead, do it in stages. Start "vith the easiest components first. For example, when rewir­ ing a condenser, start ,vith the crankcase heater or control voltage section. Wire up the control voltage and test to see if the contactor will energize. This n1ay include ,-viring up all pressure s,vitches and safety controls if they are in the con­ trol voltage section. Next, hook up the condenser fan motor. After \.Viring the n1otor, energize the condenser to determine if the fan motor is operating properly. Finally, hook up the co1npressor and test the system. This process allo,vs you to go step by step until the equip­ ment ,,vorks properly. ff there is a proble1n "vith one of the steps, it \'\11.ll be easier to solve since you kno,v ,vhat \.Viring ,-vas done just before finding the problem. It can be quickly checked, revie\.ving what was just wired. In summary, this step-by-step ,-viring approach is best ,vhen re,-viring a piece of equip1nent or in any ,viring process. Wire up and test the control voltage circuit first. Follo,-v by wiring and testing individual circuits one at a tin1e until the \.Vhole unit is ,,vorking properly.

7 .11 OPEN WIRING AND CONDUIT Open wiring is insulated, high-voltage wiring that is not in conduit or some other protective covering. Open ,viring is allow·ed in most residential installations inside the walls, attic

118

UNIT?

6

•

I 7.

8 9. 10. 11.

KEEP 30' CLEARANCE Figure 7-28 Clearance in front of a breaker panel is important for quick access to the breakers. The breaker may need to be opened to prevent equipment or personal damage.

SAFETY TIP

Figure 7-27 The arrow points to flexible conduit that supplies three-phase power to a compressor.

areas, and base1nent spaces. Overhead open ,¥iring is allo'\-ved in all types of electrical distribution systems. Som.e of the open wiring in a utility electrical distribution system is not even insulated. If a commercial building is '\-vired according to the NEC, it \-\rill not have open vviring inside the building. All ,-vir­ ing will be in n1etal or plastic conduit in all parts of the build­ ing. Figure 7-27 illustrates flexible conduit feeding po"ver to a three-phase con1pressor. Conduit can be rigid or flexible.

The technician should not hold a meter in one hand along with the two probes, one in each hand. The improper way to handle this meter is shown in Figure 7-29. using the meter on the wrong scale or a high-voltage spike may cause the meter to explode in your hand. Fewer injuries would occur if the meter were set down and not held. To reduce the risk of shock, put the meter down and measure voltage with one probe attached to one side of the circuit, while using the other probe to skip around measuring voltage. If the components are close together you can place both probes in one hand and measure voltage. That will take a little practice. If this is difficult, learn by practicing on a dead circuit. Measuring voltage with two probes in one hand is a difficult skill, and not practical if the components you are testing are more than a few inches apart.

SAFETY TIP Clearance in front of a breaker panel is important for quick access to the breakers. The breaker may need to be opened to prevent equipment or personal damage. It seems as if areas devoted to panel boxes are also mag­ nets for storage. It is difficult to keep stored items away from these serious electrical devices. Figure 7-28 shows a sign warning that 30 inches of clearance should be kept in front of the panel box. Higher voltage will require higher clearance requirements in front of the panel box. The clearance includes a clear pathway to walk up to the panel box. Stored items should be placed so that the path to the panel box stays clear. Clear panel access is required for quick service should a breaker need to be turned off in an emergency.

Figure 7-29 The tech does not have a watch or ring on when measuring voltage. Two other safe practices are not to hold the meter and to use one hand to hold two probes.

ELECTRICAL INSTALLATION OF HVACR

SERVICE TICKET

119

start with rewiring and testing a simple circuit using the following steps:

For this Service Ticket exercise, use Electrical Diagram ED-1, which appears with the Electrical Diagrams pack­ age that accompanies this text. The system you have been called to service does not work in the heating or cooling mode. The fan does not operate. A tenant has recently rented the lease space and would like the system to be in working order prior to moving into the space. After the initial inspection you notice that the wiring has been heavily modified. Wires have been spliced and some connections seem to be taped together. You have several options. The natural inclination is to troubleshoot the system in its existing state. Maybe the solution will be something simple. Yes, it is a good idea to spend a few minutes measuring volt­ ages, breakers, and system pressures. There may be an easy or obvious fix. After taking basic voltage and pressure measure­ ments, you find it difficult to determine the solution to this nonfunctioning package unit. The input voltage and transformer output voltage are correct. The refrigeration system has good pressure readings. The wiring mess and modified wiring make it difficult to troubleshoot. The second option is to draw the existing wiring diagram and use the diagram as a troubleshooting tool. Since the wiring has been heavily modified that is not the best option, because it will take a long time to develop a useful diagram. Also, errors in the drawing will prevent accurate troubleshooting. You decide to rewire the package unit according to the original electrical diagram. The tenant is made aware of the condition of the unit. She is shown the condition of the wiring. She approves a time and material bid with a limit of 2 hours to get the unit rewired and an estimate of the problem. Let's take a look at the steps that will make this a quick success. The following steps are not law and they can be rearranged for the benefit of the tech.

1. Remove all wiring from the package unit. Have additional wire and electrical connectors avail­ able. Electrical Diagram ED-1 does not list the color of wire though that would be useful. Label the wire colors on the diagram as the components are hooked up. This will be useful for future trou­ bleshooting. Placing wiring number labels on the wire and the diagram will be helpful. Figure 7-30 shows an example of how to start the numbering sequence that will aid in wiring the unit. The rule for numbering the circuit is to use the same number on all wiring points that are connected together. When the diagram has any type of change, the number will change. Going through a switch, fuse, or load would be a change. For exam­ ple, in Figure 7-30 start with the number 1 at L1. Then N (neutral leg) is labeled 2. once the power goes through the switch, the number changes to 3. When the power crosses the fuse, the number changes to 4. All wire connections on the far left side of the diagram are numbered 4. This process continues until all wire connection points are numbered. It does not matter where you start, but beginning at the power supply with a 1 and 2 is a logical starting point. 2. Between each step turn off the voltage and do the wiring. It is understood that power will be applied after each wiring step. Then test and verify operation. 3. Start with one of the easy circuits first. For example in Electrical Diagram ED-1, the crankcase heater (CH) is wired to the high voltage through the nor­ mally closed CR contacts 4 ands. The high voltage is applied and the crankcase heater warms the compressor oil. Good start!

2 N

Ll l l

4

4

CR

LP

5

5

2

HP 6

7

6

7

2

C

2

lFR 4 8 8 --11----------�

HR 4

IFM

2

1-------�2 EH

9 10 9 10 2 �----------er---r--.----------'\flA�--•2 CR

HL

Figure 7-30 This diagram illustrates how to start the numbering sequence that will aid in wiring the unit.

120

UNIT 7

4. Next, wire the primary side of the transformer to the 120-V power supply. The 24-V control voltage is measured on the secondary of the transformer. s. The indoor blower circuit is another simple circuit that can be hooked up and tested. Wire the thermo­ stat R and G connections. connection R is hooked to the hot side of the 24-V transformer; G is wired to terminals on the normally closed HR contacts. HR terminal 4 is wired to one side of the IFR coil. The other side of the IFR coil is hooked to the common side (right side) of the transformer. sometimes the common side of the transformer is labeled C. Close the "ON" fan switch on the thermostat. The con­ tacts on IFR terminals 2 and 4 should be closed. use an ohmmeter to verify that these contacts are now closed. Hook up IFR terminal 2 to L 1 and terminal 4 to the indoor fan motor IFM. Wire the other side of the motor to N. Apply the 120-V power supply. With the fan switch in the "ON" position the IFM will operate. Finally, turn the thermostat to the "AUTO" and "COOL" setting. Turn the thermostat below the room set point. The blower should now operate in the "AUTO" mode. 6. The heating circuit is a simple circuit. Wire ther­ mostat w to one side of the HR coil. The other side of the HR coil is hooked to the common side of the transformer, which is not labeled. Some wire designs ground the common side of the transformer. If the right side of the transformer is grounded, the right side of the HR coil would be grounded with no wire to the transformer. Terminal 1 of the HR contacts is wired to L1. The terminal 3 connection of HR contacts will be wired to the HL, the heater overload. The other side of HL is wired to the heat strip EH. The opposite side of EH is hooked to N. Finally, in the control voltage section, the HR normally open contacts 6 and 4 are wired. Terminal 6 is wired to left side of the thermostat and trans­ former junction. Terminal 4 is hooked to the left side of the IFR coil and terminal 4 of the normally closed HR. The other side of the IFR coil was already wired to the common side of the transformer. Keep the thermostat in the "OFF" position with the power applied. If nothing happens, proceed by turning the thermostat to the heating mode. Turn the thermostat up a few degrees above the room temperature so that the HR coil is energized. This will bring on the heat strip and indoor fan motor. Measure the amps on the heat strip. The measurement should be about 16 to 20 amps. Note: The IFR is controlled by normally closed HR contacts 5 and 4 when the ther­ mostat is in the "AUTO" position. 7. Next, the cooling circuit is wired in two steps. Wire the condenser motor first, then the compressor. 8. Hook the thermostat Y terminal to one side of the CR coil. Wire the other side of the coil to the

common side of the transformer. Wire normally closed CR terminal 4 to L 1 and terminals to one side of the crankcase heater CH. Apply power and check the crankcase heater for warmth. 9. Wire the outdoor fan motor. Terminal 4 of CR is wired to L1 and terminal 6 to one side of the out­ door fan motor (OFM). Hook the other side of the OFM to N. Turn the thermostat to cooling and test. The condenser fan should operate along with the indoor fan motor. 10. The final connection is the compressor. Wire CR normally open terminal 1 to L 1. Terminal 3 is hooked to one side of the low-pressure (LP) switch. The other side of the low-pressure switch is wired to one side of the high-pressure (HP) switch. The other side of HP is wired to the common on the compressor. N is wired to the run winding and the run capacitor. The other side of the run cap (not shown) is wired to the compressor start winding. Hook up the clamp-on ammeter to the common wire of the compressor. Operate and test. Measure the amp draw and check the system charge. This wiring method will ensure that the system will work according to the manufacturer's design. Rewiring a system without using a step-by-step procedure will lead to more lost troubleshooting time if part or all of the system does not work properly.

SUMMARY Installing power and control voltage wiring is not the major time-consuming element ,\Then it comes to installation or equipment change-out-but it is the most important step in the installation because improper ,\Tiring n1ay create a haz­ ardous condition that can cause a fire or electric shock hazard to the technician or the consu1ner. The wire size, overcurrent protection, and proper grounding are the in1portant safety aspects of good instaUation or system exchange. When doing calculations for selecting wiring and overcurrent protection, it is a safe practice to round down for overcurrent protection and round up for \-Vire size. When troubleshooting an electrical problem that involves "butchered" ,,viring, it may be easier to revvire it rather than spend time trying to figure out the problem. After removing the wiring, start by hooking up the control voltage circuit first. Test each circuit as it is \-vired. Next, hook up and test components in the high-voltage section. Start with the easiest component first. For example, if you are revviring a condensing w1it, test the control voltage circuit first. In the high-voltage section, wire the crankcase heater or condenser fan n1otor first. Proceed "vith more complex components like the compressor.

ELECTRICAL INSTALLATION OF HVACR

REVIEW QUESTIONS

121

17. Determine the MCA of a condensing unit that has a compres­

sor motor witl1 a 20 RLA and two condenser fans 1notor that draw 2 an1ps each.

1. \Vhat term is used when referring to air conditioning

efficiency?

18. Use data fro1n the nameplate shown in Figure 7-31 to answer

this question. The con.den.sing unit has been nuisance trip­ ping on its overcurrent protection device, which is rated at 40 amps. After cycling the unit a few times and checking the volt­ age, a111p draw, and pressures, everything seen1s to be work­ ing properly. \:\That would you do to reduce nuisance breaker tripping?

2. \Vhat tenn is used when referring to gas fun1ace efficiency? 3. vVhat efficiency rating number is considered acceptable for a

"green" air conditioning unit?

4. \,Vhat efficiency rating number is considered acceptable for a "green" gas furnace? 5. The U.NIC and NEC codes are developed as ______ safety standards for our industry to follow.

19. Vv'hat electrical questions need to be asked when changing out a condensing unit?

6. Describe the safest way to reset a circuit breaker.

20. vVhat is the color of a ground wire?

7. \,Vhat is the AFUE of a furnace with a Btuh output of 90,000 and a Btuh input of 100,000?

Use Table 7-4 to answer Review Questions 21 through 25. 21. In Table 7-4, what is the operating range of voltage for the

8. \Vb.at are two n1ajor things that prevent an air conditioning

460-V unit?

syste1n from operating at its peak efficiency?

22. In Table 7-4, what is the only type of wire material allowed ac­

9. Vvhat measure should be taken regarding the overcurrent pro­ tection on a replacement condensing unit?

table? cording to this 1na11ufacturer's :

23. In Table 7-4, what is the maxjmun1 fuse size that is allowed on

1 O. What comn1on electrical iten1s should be checked and sized properly when installing new· equiprnent or replacing equip­ ment?

the lv1odel S0EE-060 unit that uses 460 V and is three phase?

24. In Table 7-4, how n1uch current should a conductor carry that serves the Iv.lode] S0EE-060 unit that uses 230 V and is three phase?

11. \Vhat is the purpose of the maximwn circuit ampacity rating

on a nan1eplate?

25. In Table 7-4, how n1uch current should a conductor carry that serves the l\1odel S0EE-060 w1it that uses 230 volts and is single phase?

12. \'vhat is the purpose of the maxi1num overcurrent protection rating on a naineplate? 13. \Vhen does "nuisance" tripping usually occur?

26. Dashed lines are used in some wiring diagrams. \Vhat do dashed lines indicate to the technician?

14. \Vhat is the difference between mini1nu1n circuit an1pacity

(.NICA) and the n1aximum size of an overcurrent protection device (1'.1OCP or Jv1OP)?

27. vVhat is the supply voltage in Figure 7-30 (or Electrical Dia­ gram ED-1)?

15. Using the condenser narneplate shown in Figure 7-31, what is

28. \Vhat is the control voltage in Figure 7-30 (or Electrical Dia­

the smallest wire size you would select lo wire this unit?

gram ED-I)?

16. Using the condenser nameplate shown in Figure 7-31, what is the largest overcurrent protection device you would select to protect this unit?

29. Redraw the control voltage section in Electrical Diagram ED1. Using the nu111bering method of organizing a diagram, nun1ber the control voltage circuit on your diagra,n.

-

I CONTAINS HCFC- 22

FACTORY CHARGE 12 LBS 8 ozs ELECTRICAL RATING 1 PH

60 HZ

1

DESIGN PRESSURE HI 278 LO 144 NOMINAL 208/230 MAX MIN 197

23.8

FLA

LRA

129

HP

31 5

FOR OUTDOOR USE Vl:Dllilli_O

PSIG PSIG VOLTS

253 1 1.7 1/4

PH

RLA MIN.CKT AMPACITY AMPERAGE MINIMUM

-

FAN MOTOR(S): (1)

COMP RESSOR(S) :(1) PH

-

MAX FUSE OR CKT.BKR. FUSIBLE/COUPE CIRCUIT 50 ( HACR PER NEC)

lr-2:SJW..I

Vo;;.,�

Figure 7-31 use this condensing unit nameplate to answer Review Questions 15, 16, and 18.

122

UNIT 7

Table 7-4 Table for Review Questions 21 through 25

Model

SOEE 018 024 030 036 042 048 060 030 036 042 048 060 036 042 048 060

V-PH

208/230-1

208/230-3

460-3

COMPR LRA RLA

IFM FLA

OFM FLA

Max Fusett orHACR CKT BKR Amps

187

50.0 48.0 65.0 82.0 95.4 110.0 142.0

8.3 10.0 14.1 17.2 21.5 23.7 28.9

4.0 4.0 4.0 4.2 4.0 4.5 6.7

1.1 1.1 1.1 1.5 2.1 2.4 2.8

20 25 35 40 50 55 60

15.5 17.6 22.7 27.2 33.0 36.5 45.6

187

53.0 67.5 82.0 92.0 124.0

8.1 11.0 13.7 15.2 19.2

4.0 4.2 4.0 4.5 6.7

1.1 1.5 2.1 2.4 2.8

20 25 30 40 45

14.7 19.5 23.2 25.9 33.5

414

33.8 41.0 46.0 62.0

6.0 6.9 8.0 9.6

2.0 2.0 2.0 3.4

0.7 1.2 1.2 1.4

15 15 20 25

10.2 11.8 13.2 16.8

Oper Voltage* Max Min

253

253

506

FLA - Full Load Amps HACR - Heating, Air conditioning and Refrigeration IFM - Indoor Fan Motor LRA - Locked Rotor Amps MCA - Minimum Circuit Amps OFM - Outdoor Fan Motor RLA - Rated Load Amps *Permissible limits of the voltage range at which units will operate satisfactorily. tMaximum dual element fuse. NOTE: use copper wire only. (Courtesy carrier corporation.)

MCA

UNIT 8

Transformers WHAT YOU NEED TO KNOW After studying this unit, you will be able to: 1.

2. 3.

4.

s.

6. 7.

Describe how a transformer works. Name the types of transformers. Draw the symbols for two types of transformers. Calculate the VA of a transformer. Describe how to troubleshoot a transformer. Describe how to wire transformers in parallel. Discuss how to find a short in a control circuit.

The purpose of a transformer is to "transfonn" or change input voltage. A transformer has an input voltage and output voltage. A con11non transformer found in HVACR applica­ tions is shown in Figure 8-1. Sometimes the wnrd trans­ former is shortened to xformer. Figure 8-2 shows the electrical symbol for a transforn1er. A transformer is a device that transfers electrical energy from one alternating current circuit to another with a change in output voltage or current. Most transformers used in HV ACR reduce, or step do'.vn, the voltage being supplied. The primary winding is hooked to the incon1ing power source, and the secondary is the reduced voltage normally used in a control voltage circuit.

8.1 HOW DO TRANSFORMERS WORK? First, let's learn about the construction and operation of a transformer. The foundation of a transformer is the iron or steel core, as shovvn in Figure 8-3. The core has t'.vo sets of \\Tindings ,vrapped around it. One set of \\Tindings is called the primary winding. The prin1ary '---o......_a---�,:-_-.,.._-'� TRAN

A. SECONDARY VOLTAGE CHECK

FAN

cc COOL

COOL AUTO HEAT OFF

I I I I I

PlLOT

TH

PS

� -o 0 ROOM THERMOSTAT

TB

Figure 8-15 This diagram shows a quick way to determine if the system has an incoming voltage problem or control voltage problem. If the primary voltage on the transformer is good, check the voltage on the secondary side.

SOLUTION: For a 24-V transfonner, the voltage should drop no lower than

24 V X 10% (0.10)

=

2.4 V

So the voltage tnust be at least

ij

24 V - 2.4 V

=

21.6 V

8.6 MORE TRANSFORMER TIPS A final ,-vay to troubleshoot a transformer is to use an ohmme­ ter. There should be resistance on the primary and secondary of the transformer. The resistance is usually belo,.v a couple of hundred. oh1ns. Use the low ohn1 scale on the meter, R X 1.

It is unusual for a transformer to short to grow1d, but it can happen. Check the prin1ary and secondary ,.vindings to the transformer's steel-laminated plates or the transformer hous­ ing. Some transformers are coated ·with a protective coating that looks like a varnish. Scrape the coating off and expose an area of bare steel ,.vhen checking from the winding to ground. Use the touch test as a troubleshooting tool. A transformer ,-vill be slightly warm \\7hen fully loaded. It should never be hot to the touch. Hot transformers ,.vill soon burn out. When checking a transformer, remember the impor­ tance of the "turns ratio" we discussed earlier in this unit. For example, a 240-V pri1nary step-do,-vn transformer ,.vith a 24-V secondary ·will have an approxi1nately 10: 1 resist­ ance ratio. In other \-Vords, the resistance of the primary will be about l O ti1nes greater than that of the secondary. If this ratio does not match, there may be a winding-to-\vinding

TRANSFORMERS short. Note that the ratio will not be exact, but it should be close. You v.rill notice that in Figure 8-9 the higher voltage hook-ups have more \-vindings in series and, therefore, more resistance than the lovver voltage vvindings. Finally, .vhen \'\riring in fuse or breaker protection on the secondary side of a transforn1er, hook it to the "hot side," not the common side of the transfonner. The "hot side" goes to the R connection on the thermostat. The other side of the transformer is the co1nmon side. The common side may or may not be grounded. The ,vord con1rnon does not necessar­ ily 1nean ground or negative. It means that there are several common connection points. ((

))

.

.

TECH TIP Hook up a temporary fuse in the secondary side of a replacement transformer. The transformer may have burned out because of a short circuit or overloaded condi­ tion on the secondary side of the control voltage. Prior to wiring up the secondary of a new transformer, "ohm" the control circuit. This can be accomplished by hooking the ohmmeter to the two wires that go to the control circuit that would normally be connected to the secondary side of the transformer. If there is a short-circuit condition, the resistance will be near zero ohms. The secondary fuse should be sized for short-circuit protection. Size the fuse for 150% of the secondary amperage rating. For the 40VA transformer, with a maximum amperage draw of 1.67 amps, the fuse size should be 3 A. Many manufacturers use a 5-A fuse to protect against a short-circuit condition. This will not, however, protect against an overload condi­ tion, which is slightly above the maximum rated amp con­ dition. Some transformers, like the one shown in Figure 8-16, have built-in circuit protection. This is a resettable circuit protection, preventing damage to the transformer windings in an overload or short-circuit condition.

131

8.7 WIRING TRANSFORMERS IN PARALLEL Transformers can be \/\'ired in parallel to increase the total VA rating. This is also k110V11n as "phasing transformers." T,vo 24-V, 40-VA transformers v.1ired in parallel ,vill have an 80-VA rating. As the load on a transformer increases, the VA rating needs to increase or the transfonner ·will overheat and burn out. You can change out the transformer and install a higher rated \TA transformer or wire another transformer in parallel. lt is important to understand how to vvire the hvo transformers in parallel. \!\Tiring the transformer incor­ rectly ,vill double the secondary output voltage. For exam­ ple, a 24-V output can become 48 volts. The higher voltage output \vill burn out coils and other loads that require 24 V. Here are the steps to successfully \Vire the secondary ,.vindings ,.vithout creating a double voltage condition. Figure 8-17 illustrates ho,v two transformers are ,.vired in parallel. 1. Hook up the appropriate primary voltage to the hvo transformers. 2. Hook up one secondary '"',jre of transformer 1 to one lead on transformer 2. This can be done on a test basis using a set of ju1nper cables (alligator clips \'\'ith con­ necting ,vire) prior to the final wiring job. 3. Turn on the po\ver to the transforn1ers and read the voltage bern,een the remaining unconnected leads, as sho,vn in Figure 8-17. When po,.vered up, do not alloV11 the secondary v,rires to touch each other or ground. This will damage the transforn1er. 4. If the voltmeter reads "O V" ,.vhen connected, the con­ nection is correct. R.e1nove the voltmeter, turn off the poV1 er, and connect the final t o secondary transformer leads together. 5. If the voltmeter in Figure 8-17 reads double the rated voltage, reverse the secondary leads. You \Vill no,v read 0 V. Hook the leads together and 1neasure 24 V. Connect the two secondary leads to the control circuit. 1

1N

VOLT .tvlETER

PRI1'1ARY

---.rLINE

VOLTAGE

PRir--1ARY

- - _t_ -- --61>----..J

Figure 8-16 This control transformer has built-in overcurrent protection. The 5-amp overcurrent device protects the secondary side of the transformer winding from overloads or short-circuit conditions.

SECONDARY

SECONDARY

Figure 8-17 Phasing or wiring the secondaries of transformers in parallel is the intermediate step in measuring the final connection.

132

UNIT 8

6. Finally, double check the pow·er to the paralleled sec­ ondary ,�rinding. If the voltage is 48 V, disconnect the primary power and switch the ,-viring on secondary.

1.

TECH TIP Do not "spark" a transformer. Sparking a transformer is the practice of quickly touching the bare wires of the sec­ ondary side of a transformer together to see if it creates an electrical spark. Some techs use this as a way of deter­ mining that the transformer has secondary voltage. This may be a way to bypass using a voltmeter to measure the secondary voltage, but it is not a good practice. A trans­ former with an internal or external fuse will blow even with a quick touch or spark. Sparking a transformer is a poor substitute for a voltmeter. A spark can be created at lower, unacceptable voltage. Be a professional and use a professional's instrument for measuring voltage.

TECH TIP Some transformers have a built-in secondary trans­ former fuse that will not be obvious to the tech. This type of transformer will be identified as "fused" or "internally fused." In some instances you can remove part of the winding cover, which is paper or plastic, and expose an open fuse link. Wire in an external fuse and continue to use the transformer. This should be considered a tempo­ rary fix. Replace the transformer with a new one. Some protected transformers have a built-in circuit breaker. Reset the breaker with the power off. Power up and try to determine the reason the breaker tripped. A tem­ porary low-voltage situation will create a high-amperage condition that can trip the breaker. By the time you arrive at the job site, the low-voltage condition may have disap­ peared, but the breaker has been tripped. Reset and test.

SERVICE TICKET You are called to troubleshoot a package unit (see Figure 8-18) that is not cooling. You quickly determine that the control transformer is burned out. The transformer ap­ pears overheated and the secondary winding is open. Replacing the transformer, you install a temporary, 5-amp, inline circuit breaker similar to one shown in Fig­ ure 8-19. The purpose of the inline breaker is to protect the secondary of the transformer in case there is a short or overload in the control circuit. You plan to remove the temporary inline breaker after an operational check. As soon as the power is applied, the inline breaker trips. An inspection of the control wiring and control components does not reveal an obvious problem. Troubleshooting any HVACR system with a control volt­ age short is always a challenge. You start with these steps:

2.

3.

4.

5.

6. 7.

For the package unit shown in Figure 8-18, the first step in determining a short in the control voltage cir­ cuit is to disconnect everything from the left side of the transformer, at point 1. Powering up the primary of the transformer without it being connected in the circuit should not short out the secondary unless this transformer windings is already damaged. Using the diagram in Figure 8-18 as our example, connect one control voltage circuit at a time until the inline circuit breaker trips. The inline circuit breaker will be installed, in series, between the left side of the transformer and the R con­ nection on the thermostat. On the left side of the diagram, at point 1, hook up the R wire to the trans­ former. The right side of the transformer will also be connected. The circuit breaker does not trip. Next, close the system switch at point 2 that follows the R connection. This is the on and Off switch found on some thermostats. The circuit breaker does not trip. Now switch (close) the fan switch to Auto, point 3. The circuit breaker does not trip. TheOFR)coil and contactor coil©have been discon­ nectea'as part of the troubleshooting process. Next, you turn the thermostat temperature low enough so that the cooling circuit is closed, point 4. The circuit breaker does not trip. When you attach the�coil, at point 5, the breaker does not trip. Finally, connecting the contactor©circuit, at point 6, trips the breaker. You have established that the short circuit is in the contactor circuit. "Ohm out" the con­ tactor coil or look for shorted wiring in this line of the diagram. The ohmmeter indicates that the contactor coil measures 2 Q, which is very low for a contactor coil. Replacing the contactor solves the problem.

Finding a shorted component or wire can be a real test of your "figuring it out" skills. we just completed an exercise in finding a short-circuit problem. Eliminate as many circuits as possible by disconnecting the circuit from the transformer. Reattach one circuit at a time and apply power after each circuit is applied.

TECH TIP on older air handlers and furnaces, transformers are combined with a relay. This is called a fan center. A fan center is shown in Figure 8-20. The transformer may be permanently mounted to a plate on the fan center. A burned-out transformer will need to be replaced with a new fan center or by mounting another transformer near the fan center. The relay is usually plugged into the fan center and can easily be replaced if defective. The diagram in Figure 8-21 shows the electrical hook-up for a fan center showing the transformer and fan relay.

CRC

C

C

C011P CFMC

CFM

CH IH.1

IFR TR

�

R

LEGEND C: COMP: CRC: Cf.M: CH.1C: IFR: ITh1: HP: LP: CH: TR:

-------------------,

..---CONTACTOR COMPRESSOR COMPRESSOR RUNNING C APACITOR CONDENSER FAN MOTOR CONDENSER FAN MOTOR CAPACITOR INDOOR FAN RELAY INDOOR FAN r-.10TOR HIGH-PRESSURE SWITCH LOW-PRESSURE SVvITCH CRANKCASE HEATER TRANSFORMER

SYSTEM

0

ON

G

I I I I I I I

0

COMMON SIDE

lFR

I

AUT00

:0 I

C HP

LP

---------------------------�

Figure 8-18 The package unit shown here has a short in the control voltage side of the system. The diagram does not show the short. Troubleshooting steps are necessary. TRANSFORMER

RELAY

RESET BUTTON --

Figure 8-19 This is a temporary, 5-amp, inline circuit breaker. This should be placed on the "hot side" of the secondary of the transformer to protect it against overcurrent or short-circuit conditions.

Figure 8-20 The fan center has a combined transformer and fan relay.

134

UNIT 8

you can remove and vvire directly or better yet a permanent fuse that ,vill protect the transforn1er from a short-circuit con­ dition. Size the fuse at 150% of the secondary amperage rat­ ing to prevent nuisance blown fuses yet still protect against a short-circuit condition. This will not protect against an over­ load condition. An overload condition is one in which a higher than normal amp dra,v is occurring, which ,.vill overheat the transfonner and eventualJy burn it out. Use the touch test. A transformer ,..,ill be slightly ,varm ·when fully loaded. It should never be hot to the touch. Hot transformers vvill soon burn out.

BR O\VNNC BLACK COM1\10N

RED NO COIL

BLACK COM1\10N RED208V

0 y

C

REVIEW QUESTIONS

G

ORANGE240V R

l. Describe how a transformer works.

0

\\f

2. Name the three common types of transformers.

Figure 8-21 This diagram of a fan center shows the symbols

for the transformer, relay coil, and relay contacts. The R, c, G, w, and Y screw connects are on the transformer.

3. \Vhat are four comn1on transformer input voltages? 4. vVhat is the most common step-down transformer voltage output? 5. Does the amperage go up or down in a step-down transformer? 6. \·\That is the ma:xi1nun1 an1perage output of a 75-VA trans­ fonner on a 24-V secondary? 7. \l'v'hat information is required when ordering a replacement transfonner?

SUMMARY It is important to understand ho\v transformers operate because they are one of the first pieces of equip1nent that should be checked ,.vhen troubleshooting. If the input voltage is present, you can determine tl1at part or all of the systen1 has voltage. If the output voltage is present, you can continue the troubleshooting process on the control voltage side. This troubleshooting process ·will depend on the problem and may not be the most expedient way to proceed. It is a place to start if you do not know anything about the circuit operation. The first step to checking a transforn1er is detemlining if there is input voltage. Next check the output voltage. Some transformers burn out due to w1ki1ov.rn reasons. Some burn out due to overloading (too much current dra,.v) on the sec­ ondary side. Others burn out due to sho1ted co1nponents in the secondary side of the electrical circuit. Check for circuit overloading by measuring the amp draw on the secondary side of the transfonner. Check for short circuits or lov.r-resistance circuits \vith an ohmmeter prior to attaching the secondary of the transformer. Place a properly sized fuse in the secondary of a replacement transforn1er. This can be a temporary fuse that

8. vVhat size fuse would you install in the secondary of a 40-VA, 24-V transformer to protect against a short-circuit condition? 9. Your clamp-on ammeter n1easures no lower than 5 a1nps. How would you n1easure amperage on the secondary of a 24-VA transf.onner.? 10. The technician phases two 24-V, 40-V A transformers to in­ crease the rating to 80 VA. After the technician wires the sec­ ondary of the transformer, 48 volts is n1easured. \1Vhat does the technician need to do to obtain the desired 24-V output? 11. List three ways to troubleshoot a transformer. 12. \Vhat is the advantage of a multi-tap transfonner? 13. \Vhat is the purpose of an isolation transformer? 14. \Vhich transformer will increase the output voltage and de­ crease the output amperage? 15. A technician wants to increase the voltage output of a trans­ former. The tech wires up several input voltage leads with the hope of obtaining increased voltage. Will the tech get increased voltage? If not, what will happen to the transformer? 16. \!\,'hat type of transformer is shown in Figure 8-22? \Vhat is its voltage input?

1:2 PRI!MARY COIL 900TURNS

SECONDARY COIL 1800TURNS

AC

LOAD

SOURCE l20VAC I= IOAMPS

Figure 8-22 use this diagram to answer Review

Questions 16 and 17.

VLOt\D

= 240 VAC

I= 5 AivIPS

TRANSFORMERS

135

17. Tn the transforn1er shown in Figure 8-22, what is the maxi1num amperage that the secondary can handle?

19. Tn the transformer shown in Figttre 8-23, what is the n1aximun1 a1nperage that tl1e secondary can handle?

18. \.Yhat type of transformer is shown in Figure 8-23? What is its voltage output?

20. \Vhat wire connections are used to hook up a 480-V co1n1ner­ cial transformer?

PRIMARY COIL 1800TURNS

240VAC I= 5AMPS

2: I SECONDARY COlL 900TURNS

VLo.w = 120VAC

Figure 8-23 use this diagram to answer Review Questions 18

and 19.

UNIT 9

Relays, Contactors, and Motor Starters WHAT YOU NEED TO KNOW After studying this unit, you will be able to: 1. Describe the operation of a relay. 2. Troubleshoot a relay.

3. Describe the operation of a contactor. 4. Troubleshoot a contactor. s. Describe the operation of a motor starter. 6. Troubleshoot a motor starter. 7. Select a replacement relay, contactor, and motor starter.

The purpose of this unit is to describe the similarities and differences runong a relay, a contactor, and a motor starter. Relays, contactors, and motor starters are used to control, that is, turn on and off, an electrical circuit. They are all electric switches. They have a coil of wire that is used to magnetically and mechanically open or close a set of contacts (switches). The main difference between the relay and the contactor or motor starter is the rated amperage that can run through the contacts or switches. Relays are lO'w-amperage devices, ,-vhereas contactors and 1notor starters can handle high amper­ age through their contacts. The difference bet\-veen a contactor and motor starter is that motor starters have an overload pro­ tection device installed.. The overload protection device opens up the control circuit ·when excessive current is measured to the load. One common use of these devices in the HVACR industry is to start fan or pump n1otors and compressors. There is another class of relays that help motors start and/or run. These very specific types of relays are associated ·with specific types of n1otors. They ·will be discussed in Unit 15 on motors. They go by the names of centrifugal s,vitch, potential relay, current relay, and solid-state relay. This unit also describes ho,-v to troubleshoot these s,vitching devices and what information is needed to order a replacement part. We start by explaining the standard fea­ tures found in all of these types of s,vitching devices.

coil will energize a 1nagnetic field and the magnetic force ,vill mechanically n1ove the contacts ,-vhen the proper volt­ age is applied. A simplified illustration of this is sho\.V11 in Figure 9-1. In Figure 9-lA, the coil is de-energized and the contacts are held closed by up,vard spring force. This ·would be called a normally closed (NC) relay since the contacts are closed ,vhen the relay coil is de-energized. The coil in Figure 9- lB is energized and the contacts are opened by the n1ag­ netic attraction of the coil. These are called electro1nechani­ cal devices because they rely on the magnetic field generated by current flo\.V to mechanically 1nove a set of contacts. The spring is a mechanical force that causes a set of contacts to open or close. Some contacts are gravity operated in the de­ energized n1ode. They will close by the force of gravity. These

(A)

9.1 COMMON FEATURES The relay, contactor, and motor starter have many con1mon features. This section explores these si1nilarities.

Coil Voltage All of these control devices have a coil of ,vire that is en­ ergized to magnetically open or close a set of contacts. The 136

(B)

Figure 9-1 (A) This is an example of normally closed contacts. (B) Here the normally closed contacts are shown switching position when the coil is energized.

RELAYS, CONTACTORS, AND MOTOR STARTERS

types of contacts n1ust be mounted in a specific direction to make use of the gravity field. Common coil control voltages are 24, 120, 208, or 240 volts. If the control voltage is too lo\v, it \Vill not generate enough magnetic force to change the position of the device. For example, if a 24-V coil has 18 volts applied to it, it n1ay not operate the device. Low voltage on the coil could cause the mechanisrn to "chatter." Chatter occurs \Vhen the volt­ age to the coil is low and the coil creates just enough magnet­ ism to operate the mechanism. The word chatter comes from the rapid closing and opening of the contacts, \Vhich creates a chattering noise (like the chattering of teeth \Vhen a person is cold). Very lo,v voltage wiJJ not create chatter since there is not enough magnetic force to operate the contacts. A chatter relay is unnerving and noisy. High voltage on the coil \vill cause the coil to overheat and burnout. Son1etimes voltages in a system get crossed. For example, a 24-V control circuit accidentally con1es i.n contact ,vith 120 volts. The higher voltage will burn out the 24-V coil quickly. Check the coil voltage before replacing a con1ponent that has a burned-out coil.

137

Table 9-1 Basic Rating Information for a Relay The label found on the side of a basic relay includes important information such as coil voltage, contact amperage rating, and maximum contact amperage rating. Manufacturers may arrange this information differently, but the coil voltage, rated load amps, and operating voltage are all important parts of selecting a relay.

Relay #ABC123 24-Volt Coil Low-current, Magnetic Switch contact Ratings AFL

ALR

Voltage

11 amps

73 amps

120 volts

5.5 amps

35 amps

277 volts

3 amps

17 amps

480 volts

16 amps resistive

277 volts

10 amps resistive

480 volts

-

Number of contacts Each device has one or more movable contacts or S½�tches. The contacts may be normally open (NO) or normally dosed (NC). They are represented in electrical diagra1ns by the syn1bols shovvn in Figure 9-2. Figure 9-2 show the relay symbol for one normally open contact, one norn1ally closed contact, and a relay coil. (Other symbols for a coil are al.so used, such as a circle or the letter C inside a circle.) Replace1nent co1nponents ·will need to be selected to n1eet the nun1ber of required contacts. For example, a relay may have a normally open (NO) and a normally closed (NC) set of contacts. One or 1nore contacts .may be open, vvhile other contacts 1nay be dosed. It is acceptable to replace a con1ponent that has one contact \Vith one that has extra con­ tacts; the extra contacts ,vould just not be used.

Rating of contacts Contacts are t,vo semi-rounded surfaces that strike together to close and create a con1plete circuit. The contacts are usually silver plated for good electrical conduction and long life. The contacts are rated by the voltage and amperage they can carry.

-"vFigure 9-2 These are the symbols for a simple relay with

one normally open contact (top), one normally closed contact (middle), and a relay coil (bottom).

A typical label, like that sho,vn in Table 9-1 for Relay #ABC123, provides important information about the relay. Using the label ,ve can determine the follovving information: lt has a 24-V coil and is listed as a low-current, magnetic s,vitch. The three colun1ns are contact amperage ratings. These are per pole or per contact set ratings. Starting ,vith the left column, the contact ratings is stated as AFL or amps full load. This is also knovvn as rated load a1nps or RLA. This is the maximum amperage operating through the contacts at 120 volts. The 120-V rating is shown in the far right col­ wnn. A load operating above this amperage level may ,.veld the contacts closed or simply burn out the contacts. The 1niddle column is listed as ALR or amps locked ro­ tor. This is con1monly kno,vn as locked rotor amps (LRA). The phrase locked rotor amps refers to the condition in ,vhich very high amperage dravv is occurring. This condition is found \Vhen the motor first starts or \vhen the motor is n1e­ chanically locked up and cannot rotate. You will notice that the ALR is about six ti1nes higher than the AFL. It is normal for the starting amps or ALR to be this high for a brief second on start-up. If the n1otor stays at the locked rotor a1nper­ age draw for n1uch longer than a fe\.v seconds, the overload protection device ,vill open the circuit and de-energize the coil or power to the motor windings. A relay like this may have tv,o or rnore normally open contacts and t\vo or more normally closed contacts. These options allovv for many dif­ ferent control options. Table 9-2 illustrates common information found on a contactor. This is for a double-pole generic contactor, Contactor #XYZ123. As shown on the label in Table 9-2, the coil operates on 24 volts and is listed as a high-current, mag­ netic s,.vitch. The information found on the nameplate is a per pole contact rating. Table 9-2 has three columns that relate

138

UNIT 9

Table 9-2 Basic Rating Information for a common Two­ Pole Contactor

The label found on the side of a common two-pole contactor shows the coil voltage and operating current conditions under various voltage inputs to the load. AFL means amps full load or maximum running amps. ALR means locked rotor amps, also known as starting amps.

Contactor #XYZ123 24-Volt Coil High-Current, Magnetic Switch Per Pole contact Ratings AFL

ALR

Voltage

28 amps

120 amps

277 volts

12 amps

55 amps

480 volts

8 amps

34 amps

600 volts

48 amps resistive

--------

277 volts

40 amps resistive

--------

480/600 volts

to the voltage and amperage dra,.v allo\ved on each pole. The far right column sho\vs the range of volts. For example, the first voltage row is O to 277 volts. The second r0\'\' is 278 to 480 volts, the third ro\V is 481 to 600 volts, and so on. AFL refers an1ps full load or the amps the systen1 operates at when running at normal capacity. This is con1monly stated as rated load amps (RLA). The center column sho,-vs the ALR or a1nps locked rotor. As with the relay, you ,.vill notice that the ALR is about five or six times hi.gher than the AFL. As mentioned earlier, it is normal for the starting a1nps or ALR to be this high for a brief second on start-up. Ren1ember, ho\'\rever, that if the n1otor stays at the locked rotor amperage condition for much longer

than a few seconds, the overload protection device will open the circuit, preventing the 111otor fron1 starting. The bottom two rows in Table 9-2 deal with amp dra,,v in resistance an1perage (amp res) circuits. A resistance an1ps circuit is a circuit that handles electric strip heat or incandes­ cent light loads. Most of the loads in }IVACR are inductive, not resistive. Inductive loads include n1otors, relay coils, or transformers. Inductive loads dra,,v high mnounts of starting amperage con1pared to resistive loads. Selecting the right amperage rating for the contacts is important. You can install a relay or contactor ,\Tith a higher an1perage rating if necessary. A high-amperage contactor "¼'ill cost more because the contacts are larger and design ed to handle higher amperage. In summary, to select a replacement relay or contac­ tor, you need to know the coil voltage, number of contacts, rated amperage rating on the contacts, and the type of load, ·whether it is resistive or inductive. Figure 9-3 sho,vs a rat­ ing label on the side of a contactor. You ,..rill need to kno\v the operating voltage and operating amperage to select the correct replacement. A larger amp rating is acceptable. A re­ placement contactor v,ith a smaller an1p rating v,rill quickly burn out the contacts. The label also usually states the coil voltage. It lists information si1nilar to that given in Table 9-2.

9.2 DIFFERENCES AMONG RELAYS, CONTACTORS, AND MOTOR STARTERS The n1ajor difference bet\veen a relay and a contactor is the amount of current a relay contact can handle. A relay is considered to be a low-current s,.vitch. Low current in this case 1neans the relay contacts handle less than 15 an1ps. Contactors and n1otor starters handle much higher am­ perage. Relays nonnally have one or more normally open

Figure 9-3 Note the rating label on the side of

this contactor. A closer view is shown in Table 9-2.

RELAYS, CONTACTORS, AND MOTOR STARTERS

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c;''

ii

I

I

•

.

•

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component. This section sho,vs you how to conduct simple checks on the suspect component.

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•

'

ll

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Check the Coil

••

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-

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fl •

139

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Figure 9-4 Top view of a common relay. Some contacts are NO and some are NC.

(NO) contacts and one or more normally closed (NC) con­ tacts. Contactors and motor starters have normally open contacts. The coil voltage is normally 24, 120, 208, or 240 volts. Figure 9-4 is a common relay used in the HVACR industry. lt has NO and NC contacts. Notice the contact symbols em­ bossed on the relay surface. There are NC contacts bet\-veen connections l and 2, and NO contacts ben"7een connecti.ons l and 3. In Figure 9-5 ,-ve sav.r that the fan relay and contactor are wired \vithout regard to the location of the component parts. This can be a bit confusing since the con1ponent parts of the relay or contactor are one, yet they appear to be sepa­ rate when looking at an electrical diagram like the one shovvn in Figure 9-5. Finally, there are several configurations of relays. A common type was introduced in Figure 9-4. Some relays plug into a socket. .Ivlany of the socket-type relays have a clear plastic case over the1n, so you can see the coil and contacts. These are sometimes called ice cube relays since they have a clear case and are relatively cubical. Another type is n1ore difficult to identify. Those are relays mounted on a circuit board. They are small and not identified by the n1anufacturer.

9.3 RELAYS Several things can go ,-vrong ,-vith a relay. You ,vill use an oh1nmeter and/or voltmeter to troubleshoot this device. When troubleshooting a relay, it is ren1oved fron1 the circuit so that the technician can safely check the relay condition ,'\rith an ohmmeter. A voltmeter may be used if the ohn11neter does not reveal a problem. As discussed in Units 26 and 27, the hopscotch trou­ bleshooting method should be used to isolate a problem

Coil resistance is usually lo·w, less than a 1 kfl ( :5 l ,000 ohn1s). Most coil resistance is around 100 fl or less. As you '"'ill learn in other units in this teA't, some specific-purpose relays have a much higher coil resistance, so1ne as high as 6 k!!. A coil with a fe,-v ohms n1eans the coil vvire is shorted and ,vill not develop enough n1agnetic strength to operate the relay contacts. A coil with a few ohms of resistance may create a high amperage condition and burn out the second­ ary of the transformer. lf the coil appears burned, it will be open or shorted. Lovv resistance in a circuit creates a high amperage dra,"7.

Check the contacts Next check the contacts. Normally closed (NC) contacts should measure O fl. Resistance on closed contacts means the contacts have a carbon buildup, vvhich creates resistance even ,vhen the contacts are closed. Resistance on closed con­ tacts could also mean that the closing mechanis1n (spring, magnetism, or gravity) is not holding the contacts tightly closed. Replacement is required. Normally open (NO) contacts should read infinity. Any resistance indicates that the contacts ai-e mechanically stuck or ,-velded closed. Replacen1ent is required. Many relays have extra, unused contacts. If a set of con­ tacts becomes defective, another unused set on the relay may be used. If the ohmmeter check does not reveal a problem, you v.rill need to troubleshoot the relay "hot," n1eaning with voltage applied. First, 1neasure the voltage applied to the coil. The proper coil voltage will cause the contacts to S\vitch position. In a moderately quiet environment, you can hear the relay click and change position when the coil is energized. Remove the voltage from the side of the coil and place the ,vire back on the tenninal to hear the relay dick and change positions. The clicking sound does not guarantee that the contacts are changing position. Lo,v coil voltage ,-vill cause the relay to "chatter" or rapidly open and dose positions. When the coil is in a de-energized state and "''ith voltage applied to an open contact or switch, a voltme­ ter ·will read the applied voltage in that circuit, as sho,vn in Figure 9-6. When the coil is energized, the contacts or switch ,-vill close and the voltmeter reading ,-vill drop to 0 V (see Figure 9-7). Next, test the norn1ally closed contacts. When the nonnal voltage is applied to a closed set of contacts, the volt1neter reading ,-vill be O V, since a closed contact is the same as 1neasuring voltage on a single piece of ,-vire at the sa1ne potential. v\Then the relay coil is energized, the contacts open and the applied voltage will be measured

140

UNIT 9

SEQUENCE OF OPERATION 9.1: RELAY AND CONTACTOR LOCATION The electrical diagram in Figure 9-5 shows relay and contac­ tor locations. It is important to understand that the contacts and coil are found in one component but are located in

different parts of the diagram. The fan relay coil is located in the lower right, control voltage section. It is labeled IBR and highlighted in tan (see point 1 in Figure 9-5). The relay

0

0 COMP

cc

cc

L---O-�OUTDOOR 1--o----' FAN

HR

HR

-------

e:

INDOOR FAN

______ , _J

IBR

240V

R'.J---------------0----1

24 V

HR

HEAT

o

OFF

COOL

ON

o o-----.-----Vay to check a capacitor is to use a capacitor checker. Many quality DMMs have a built-in capacitor checker option, as shoVl'Il in Figure l 0-11. The capacitor should be within + 10°/4 of its labeled 1nicrofarad rating. S0111e manu­ facturers have a range as lo,-v as +5%. Look at the capacitor label .

..

CAPACITORS

159

Figure 10-10 A run or start capacitor can become swollen or explode, which makes it unusable.

(A) RUN CAPACITORS

(8) START CAPACITOR

NOR.tvIAL

FAIL SAFE MODE

PHYSICAL INTERRUPTER (C) CAPACITOR SAFETY FEATURES

to detennine the acceptable range. Start capacitors have a range printed on the label. For example, you might see "88-108 MFD." The microfarad rating should not fall outside this range. A weak capacitor may prevent the motor from starting or, if started, may dra,-v high an1ps and cause the motor to cut out on overload. Some techs use the ohmn1eter to check a capacitor. Placen1ent of the ohmmeter probes on the capacitor actu­ ally charges the capacitor so that it reads near O .n for a sec­ ond or tvvo. After a brief 111oment near the 0-!! reading, the

Figure 10-11 A capacitor should be checked with a capacitor checker.

resistance reading drifts to\.vard infinity (oo). The lovv resist­ ance reading sho,-vs that the capacitor is charging or receiving electrons fro1n the battery in the ohmn1eter. After the capaci­ tor is charged, it stops receiving electrons and the ohmmeter reading increases to,vard infinity. This is best done ,,11th an analog (needle 1novement) ohmmeter. It can be done ½rith a digital meter, but the readout is 1nore confusing. Even if a capacitor sho,vs a charge using an ohm1neter, this does not tell the technician the microfarad rating of the con1ponent. The capacitor can be off by more than 10% and sbo,v a charge condition. The ohmn1eter is good to check for a grounded metal case. Test each terminal to the case. The ohmmeter reading fron1 the capacitor terminal to the metal case should be infinity at all times. One side of the bleed resistor needs to be ren1oved ,vhen checking a capacitor \Vith a capacitor checker or ohmn1eter. If the bleed resistor is not removed, the meter reading lvill indicate a short or the resistance of the bleed resistor. rf the capacitor is still usable, the bleed resistor should be installed back on the capacitor prior to operation. Careful planning when ren1oving the resistor will n1ake it easier to reinstall it ,-vhen the job is finished. A dual capacitor is checked differently than a single ca­ pacitor. Check each side of the dual capacitor for the cor­ rect n1icrofarad rating and case ground. One section of the capacitor can be good while the other is defective. The good section can continue to be used, ,.vhile the defective section can be replaced by a separate, second capacitor. Support the replacement, single-rated capacitor so that it does not dangle by it ,.vire connections. Another device that is useful when troubleshooting ca­ pacitors or motors is the multiple capacitor set, as sholvn in Figure l 0-12. This is available as a start or run capacitor set. The multicapacitor set can be used as a temporary capacitor substitute. The capacitors in this device can be ,vired in series or parallel to decrease or increase capacitance. (This option is discussed in the next section.) Also, having the option to vary

160

UNIT 10 IO µF

10 µF 5mfd • (6.0mfd)

7.Smfd

0

£11g1. 11eer111g, . lnc

••n R d,onoc Co ,Inc., Palm Coal1

bci2 """ 1939"

A\I \R "\.D

E11gi11et•ri11g, Inc Co Inc . P•'"' C\'S the user to bypass the programmed settings until the user releases the override button again. Some over­ ride functions have time limits. For e,xample, pressing the override function may allow bypass of the progra1n for sev­ eral hours. After the override time period, the thermostat reverts to the programmed time settings.

11.15 PROGRAMMING OPTIONS Thennostats offer several programming options, depending on their design: ■ The 5-2 programming option ■ The 5-1-1 programming option ■ The 7-day progra1nming option (see Figure 11-31). One co1nmon option is the 5-2 day. The "5" represents Monday through Friday operation and the "2" the vveekend

Sun Mon Tue Wed Thu Fri Sat

_,.

•-· PM

:1 ·I_IC

,--,-,,,-,,:, -, HEAT

TEMP

Figure 11-31 This programmable thermostat offers the 7-day

option. This is the most versatile time setting thermostat. It gives the user a setback option for each day of the week.

days of Saturday and Sunday. In the 5-2 design, Monday through Friday have program1ned times and temperatures that are all the same. The Saturday and Sunday temperature settings are the same. With homes occupied on an irregular schedule on the weekend, the homeo,-vner n1ay not ,�rant to change the thennostat setting for these days. In other \.Vords, they ,vould leave them unprogra1nmed. This ,vould leave the te1nperature at whatever setpoint is selected throughout the whole weekend. If the 5-2 thermostat is used in a business building that is unoccupied on '\>Veekends, a setback tempera­ ture may be programmed to save energy. Son1etimes changing the ten1perature for 2 days presents a challenge to the heating or cooling systen1 to create a con1fortable setting when en1ployees arrive on Monday. In this case, it is best to have the syste1n start up at least an hour before the occupants arrive. The 5-1-1 option programs Monday through Friday on the same setpoint tin1es, but then Saturday and Sunday can be prograinmed differently. A 7-day progran1mable thermostat ,-vill allo\\T the home or building occupant to change the temperature setpoint for each day of the ,veek. The 7-day option can handle the n1ost irregu­ lar schedule. This thermostat is the most flexible of the group.

SAFETY TIP Many thermostats have cooling time delays. Once the cooling system or heat pump cycles off, there will be an approximately s-minute time delay before it cycles on again. This is for the protection of the compressor. The time delay allows the pressures in the system to equalize for easier starts. The time delay also allows the power fluctuation to level out prior to starting the compressor. This is a good option for most pieces of refrigeration equipment.

SAFETY TIP Wiring two control voltage transformers together is called phasing transformers. A few systems use two transformers to control the heating and cooling circuits. Some transformers are wired in parallel to improve their

THERMOSTATS

volt-amp (VA) rating. For example, if you need a 60-VA transformer, phase two common 40-VA transformers in parallel to create an 80-VA rating. The 80-VA rating will more than handle the 60-VA requirements. The primary windings and the secondary windings are hooked up in parallel to develop the 24-V output. Miswiring the sec­ ondary can also create 48 volts. A 48-V output will dam­ age most 24-V components. Check the voltage output after wiring transformers in parallel.

11.16 DUMMYTHERMOSTAT "Dummy'' thermostats are sometimes used to satisfy the

personal need to control a thermostat; they do not control anything. A dummy t'stat is installed, at the customer's re­ quest, ,.vhen the occupants of a home or business "play 'Nith" or continually adjust the thermostat. This is especially true if the thermostat is in a common area ,-vith easy access for fiddli11g v,ri.th the settings. The system will still have a preset (preset for heating and cooling) thermostat mounted in the return air duct or other area that is hidden or unkno\ivn to the users in the space. Dumn1y thermostats are 1nore con1mon in the business environn1ent than the home environment be­ cause businesses have more individuals i.n a given space ,vi.th a wide variety of comfort zones.No one temperature ,-vill satisfy everyone; therefore, each individual v,rants to change the ther­ mostat to accom1nodate his or her particular comfort level. The dummy t'stat works on the "placebo effect." In this case, the placebo effect of adjusting the temperature satisfies the desire to control the area temperature.

SAFETY TIP In most cases it is not good practice to completely turn off the thermostat. The heating and cooling systems need time to recover to meet the temperature setpoint on the hottest and coldest days. Occasional conditioned air circulation will keep the indoor air from becoming stagnant. In the summer season a periodic cooling cycle will reduce mildew, mold, and moisture buildup in the bathroom, kitchen, and laundry room.

185

GREEN TIP Did You Know? ..I -

IM!Bi!tfliM;I The Energy Star website states that the average household spends more than $2,200 a year on energy bills-nearly half of which goes to heating and cooling. Homeowners can save about $180 a year by properly setting their pro­ grammable thermostats and maintaining those settings. The $180 savings assumes a typical, single-family home with a 10-hour daytime setback of 8 °F in winter and setup of 7° F in summer, and an 8-hour nighttime setback of 8 °F in winter and a setup of 4°F in summer.

The preprogrammed settings that come ,vith program­ mable thermostats are intended to deliver savings ,vithout sacrificing comfort. Depending on your customer's sched­ ule, they can see significant savings by sticking ,vith those settings or adjusting them as appropriate for their fa1nily's particular schedule. The key is to establish a progran1 that automatically re­ duces heating and cooling in a home v.rhen the occupants do not need as much conditioned air. Table 11-2 sho,vs the Energy Star recommendations for a progran1mable thermostat.

SAFETY TIP Working on a thermostat has killed many transformers! crossing or touching the control wires together too long will create high amperage in the transformer and burn it out. You can avoid this by placing a fuse in line with the secondary of the transformer before you work on the thermostat. For the common 40-VA transformer, use a 5-amp fuse. The maximum amperage load a 40-VA transformer can handle is 1.67 amps. The 5-amp fuse is selected to protect against a direct short and not an overload condition. Make up a fuse holder with alligator clips on each end. Temporarily wire this series with the hot side of the secondary of the transformer while working on the ther­ mostat. A blown fuse is easier and cheaper to change than a transformer.

Table 11-2 Programmable Thermostat Setpoint Times and Temperatures setting

Time

Setpoint Temperature (Heat)

Setpoint Temperature (Cool)

Wake

6:00 a.m.

78° F

Day

8:00 a.m.

Set back at least 8 ° F

Set up at least 7 ° F

Evening

6:00 p.m.

78 ° F

Sleep

10:00 p.m.

Set back at least 8 ° F

Set up at least 4°F

Note: The author does not agree with all of these recommendations. Most customers would not tolerate the Sleep and Setpoint temperatures for cooling. For instance, turning up the cooling temperature 4 °F when many customers want it cooler at bedtime is difficult to recommend. At best, keep the sleeping temperature the same as the evening temperature. Many customers like it a little cooler when they sleep whether it is summer or winter.

186

UNIT11

11.17 THERMOSTAT DIAGRAMS

the bottom of diagram. It is labeled in the rectangle as R W G Y. Belov.1 the 24-V transfonner is an insulated plate that has connection points for R, C, G, W, and Y. The rectangular R W G Y thennostat connection point has ·wires running to the:

This section takes what you have learned about them1ostats and applies it to con1plete diagrams like those you will see in the field.

■ ■ ■ ■

connection and Control Points Figure 1.1-32 does not show the thermostat diagram, but it does sho,v all the connection and control points. The ther­ n1ostat ,-vire connect terminals are found in the rectangle at

R to the transformer (red) W to the gas valve (white) G to the fan relay coil (green) Y to the air conditioning condensing unit contactor (yello,v).

HIGH VOLTAGE

,v I

,

}

120V-60 Hz

LlNE

DISCONNECT S\VITCH

--I

NEUTRAL HU1\11D1FIER C

FUSE

--• CIRCULATOR SWITCH

-

ELECTRONIC AIR • CLEANER

-

A J \

,� :, L.::.J

-

•

FAN S\VITCH

BRN

@

-

•

B

BLOWER MOTOR

-

B

2

/_

I

L.:::J

I R

14

3 PLATE-l'vIOUNTED

RELAY/TRA1"1SFORrv1ER

LI11JT SWLTCH

1 6

R/Y

w

'%, S',o . ��o'-11> .

_!

\ cP � �

-

I

I

s'?

L.::.J

�-

. .. .. .. .. INSUL ATED BASE

LOW VOLTAGE

. . .. . 24V -...-..,

�

40VA ./ ) I R C

-

GAS VALVE T H-TR 0 TH TR (",

1

-'"")

•-

-

-

-

•-

G \V

7 / V

THER!v10STAT

ffi ON SlNGLE SPEED tvlOTORS CONNECTY

AND R/Y '\v1RES TO LINE LEAD OF MOTOR

R

y 0

V'

V

w

I

V

G

. .......

RELAY COIL

-

-,..I ....

-

1-

.... ....

b

y

@J CONNECTIONS lN FURNACE "J" BOX

,

AIR-CONDITIONING CONDENSING UNIT CONTACTOR

B-BLACK G-GREEN R-RED V-VIOLET W-\VHITE Y-YELLO\V BRN-BRO\VN R/Y-RED \VITH YELLO\V STRIPE

Figure 11-32 The thermostat connections are located at the bottom, center of this diagram. Trace out the control circuit starting with

R to W; then R to G; and finally R to Y.

THERMOSTATS

187

SEQUENCE OF OPERATION 11.5: THERMOSTAT COOLING MODE Next, let's trace the cooling mode operation using Figure 11-33. (A larger version of this figure appears as Electrical Diagram ED-2 in the Electrical Diagrams package that ac­ companies this book.) A few notes before we begin: Notice that the supply voltage in Figure 11-33 is three phase, 480 v, and the control voltage is single phase, 120 v. The RCSTAT is a manual hand switch that can be placed in the Fan on, cool, or Off position. In the Off position with power still supplied, the control transformer and crankcase heater are the only two components that are operating. In the Fan position, the cooling system will not operate. The blower runs continuously by energizing the @ coil, which closes the three-pole EF contacts feeding power to the evaporator fan motor. The RCSTAT's normally open contacts are found on the left side of the control voltage diagram inside a rectangular box.

O Manually switch RCSTAT to the Cool operation, point 1. @

e

This closes the Cool contacts at point 2 and found in the RCSTAT box. Sending power to the� coil at point 3. The� relay coil between 7 and 8 energizes when the RCSTAT is closed.

To the right of the RCSTAT box, contacts 3 and 5 bridge the Fan and Cool circuit so that the evaporator fan cy­ cles with the cooling system.

Q

In the Cool position, power goes from the left side of the control voltage through RCSTAT and the � coil and up through contacts 5 and 3. Power through contacts 5 and 3 energizes the@coil at point 5. This closes the evaporator fan motor three-pole contactor and starts operating the evaporator fan motor.

O The EF coil also closes@contacts 13 and 14 found below the RCST AT box at point 6.

EF contacts 13 and 14 are closed and this is in line with O the©coil, found below the RCSTAT box, point 6. The ©coil at point 7 will be energized when EF and R1 are closed. When the©coil energizes, the three-pole Com­ pressor #1 contactor will close, turning on the compres­ sor. The c contacts 13 and 14 (near point 6) in the LSV line (liquid line solenoid coil) will also be energized when the ©coil is energized.

O When the LSV is energized it will open the liquid line,

allowing refrigerant to flow to the liquid line and evapo­ rator. The evaporator pressure will begin to rise rapidly. The compressor will begin to operate when the low­ pressure switch, LP, closes.

O The� coil closes R1 (point 4) contacts 3 ands (to the n

right of RCSTA plus another set of� contacts 4 and 6.

��� 150VA

120V

0--------------------------------------,

2A

-----1 I FAN I

----�--��--�---I a

1

I IV I COOL

I I

----�--*r--�----

RCSTAT

:

I

1

IRCTSTAT I .--:•

EF

L ____

14

13 C

13

LP

9

0

DTS

TS

TD

6 -o-r-o-®-T·®-T-@1--1

I (5l\1IN) 2

e

FANON RCSTAT

�

96

---+-----£§--•-@--------------7

OFF

95

------------------�&-------------

14

17

COOL

0

8

Figure 11-33 This is the control voltage section of enlarged Electrical Diagram ED-2 found in the Electrical Diagrams package that

accompanies this book.

2

188

UNIT11

Tracing tip: When tracing a \-viring diagram, cover it with a clear page protector and use erasable markers to trace the circuit. Change the color of the marker \>vhen crossing a load. Using Figure 1 J -32, trace the diagram one control cir­ cuit at a ti1ne. Trace the thermostat being closed to operate the heating circuit. This ,vill create a connection betvveen R and W on the thern1ostat connection board at the bot­ tom of the diagra1n. When tracing this circuit start at R, go to the left, and up to left side of the transformer. The po,v, er ,"7ill exit through the right side of the transformer co1nmon (C) and travel to TR on the gas valve. The 24 V will then travel through the gas valve coil. This opens the gas valve and the pow·er leaves through the TH connection to con1plete the circuit to W on the insulated base and back to W on the thermostat. Next, trace the R-to-G connection. This will energize the relay coil and start the fan operation. Finally, the R-to-Y connection ,,vill energize the air con­ ditioning unit contactor. Of course, the thermostat \Nill not energize the heating and cooling n1ode at the same time. If this happens you have a defective thermostat or control ,vires touching each other. In summary, energize the heating (W), fan (G), or cool­ ing (Y) circuit; po,ver w·ill be provided fro1n the transformer to the thern1ostat to the R connection. Here is ho,v the po,ver through the thermostat will operate each of those separate systems: Heating operation R to W Fan operation R to G Cooling operation R to Y. Using Figure 11-33, the follo,ving safeties and s,vitches must be closed in the© coil circuit in order for the compressor to start: ■ ■ • ■ ■

LP switch is closed (low pressure). DTS switch is closed (discharge temperature switch). TS is closed (thermostat). TD is timed out for 5 minutes (time delay). Contacts 95 and 96 are normally closed safety con­ tacts that are not controlled by components on this diagram.

Finally, C contacts 13 and 14 provide a parallel path to coil ©- Coil© \\'ill control an air-cooled or \\'ater-cooled condenser. The condenser section is not shown on this diagram. A note on UL: UL is part of an unloader circuit, but not part of the thermostat electrical control circuit. The unloader is a refrigeration flo-w control device. The unloader reduces the refrigerant in circulation when the cooling de1nand is re­ duced. Son1e unloaders are energized ,vhen system capacity is reduced, ,vbereas others are energized at full systen1 refrig­ eration capacity.

0 Figure 11-34 No thermostat display. No control voltage.

11.18 GENERAL TROUBLESHOOTING STEPS Detennining if a malfunction is in the thermostat, control \'viring, or another co1nponent is not difficult. Here are trou­ bleshooting steps that v.rill be helpful: 1. Use the ACT method of troubleshooting, which ,vill be explained in detail in Unit 25, How to Start Electrical Troubleshooting. Here is a sumn1ary of the ACT n1ethod: The ACT method of troubleshooting means you are going to check the duct and condenser airflo,v (A), the compressor operation (C), and the thermostat setting (T) to help you narro,v down the problen1. 2. If it is a digital thermostat, does it have a display? If there is no display as sho,\Tl1 in Fi611.rre 11-34, check the 24-V trans­ forn1er output. If there is no transforn1er output, check the input voltage as sho·wn at points in Figures 11-35 and 11-36. If no input voltage is present, trace the prin1ary ,vire back until you find the reason for the loss of po,ver. The input po\\rer is usually 120 or 208/240 volts. To recap: No display c>Check transformer secondary c> No voltage, check pr.i1nary and voltage source 3. Turn the thern1ostat off and on. Adjust the setpoint sev­ eral degrees above the room te1nperature for heating and several degrees belo,.v the room temperature for cooling. 1'1any thermostats have a S-n1inute time delay after the system is turned off. Inspect the equipment ,vhile wait­ ing for the timing sequence to time out. In rare cases of "operator error," the setting or setpoint ,vill be the only problem, in ·which case, cycle the system several times before you leave the customer. Allow the thern1ostat to reach a setpoint and shut do,,vn. You do not ,vant to be called back because of an intermittent proble1n. 4. At this point the problem is most likely the thermostat or control ,,riring. Figure 11-37 sho,,vs a ,vay to isolate the proble1n. Remove the t'stat and expose the control ,vires or the subbase. \!\Tith a jumper, go from R to G. This \\�ll

THERMOSTATS

189

NO VOLTAGE ON THE SECONDARY

�I I

Figure 11-36 No voltage on the primary of the transformer.

Figure 11-35 No voltage on the secondary of the transformer 230V R 24V

I

FAN RELAY COIL

I

I

1

'-

I \

I I \

-0

''

G

-----

I I

l----------------1

INSULATED JU!vtPER \1/IRE FROM HOT R TERJ\tIINAL \

'

,_

--- ------------- ---

ROOM THERl'vtOSTAT BOUNDARIES �

0 y

--

I I I I I

Figure 11-37 This shows a troubleshooting process. Remove the thermostat and use a jumper wire to check each circuit. Jumper from R to G to check the blower section. Jumper from R to Y to check the condensing unit operation. Jumper from R tow to check the heating circuit operation.

COOLING RELAY

corL

HEAfRELAY COIL

- -,

"'- \V : --------------------------------------

operate the blo\ver. It ,-vould be best to leave the blov,rer operating throughout the ren1aining troubleshooting se­ quence. Next, ,"1ith a jumper \'\rire, go from R to W. This ,.vill operate the heating system. With a jumper wire, go from R to Y. This v,rill operate the cooling syste1n. 5. If the ju1nper activity operates all of these systems, then the thermostat is defective and the connecting wires are all good. If one jumper does not make the syste1n operate, it is an open thermostat vvire or some other component issue in that line. Be patient ,vhen using this jumper sequence. Some of these circuits 1nay have a S-1ninute time delay that is not part of the t'stat. Timed circuits are commonly found in cooling circuits. 6. Finally, you can troubleshoot the thermostat directly. Remove the thermostat (and subbase if it has one) fro1n the ,.,all and disconnect all thermostat ·wires. \Vith an

ohmmeter, check the continuity bet,-veen R and the other connections G, Y, and W. Test one circuit at a tin1e w1til all the circuits have continuity. Remember to s,-vitch the circuit you are testing. For exan1ple, if you are testing the cooling circuit, make sure the thermostat is set to cooling and the ten1perature is turned do,-vn sev­ eral degrees belo"v the setpoint. The resistance should be near zero ohms, except for the W connection, which may have some resistance through a heat anticipator. The heat anticipator is a high-resistance heater ,,rire. \Vhen checking a mechanical t'stat, it v.rill need to be level. Digital thermostats require batteries or some other power source. You do not want to measure battery volt­ age ,'\1hen your meter is in the Ohms range. You \\rant to measure the t'stat switches. Measuring voltage ,,vill blow the meter fuse or dan1age the n1eter.

190

UNIT11

SAFETY TIP Many older mechanical thermostats use a mercury switch. Mercury is considered to be a hazardous mate­ rial. Mercury-containing thermostats must be recycled. Many HVACR supply houses are recycling centers for mercury thermostats as shown in Figure 11-38. Do not throw mercury t'stats into the trash. They can pollute landfills and drinking water.

the circuit board reveals that it has a 3-amp, plug-in type fuse. The fuse appears to be in working order but when checked with an ohmmeter, it is found to be open. Before replacing the fuse you go back to the thermostat and make sure there are no shorted wires at the connection points or nicks in the wire insulation. No shorts are found at the ther­ mostat location or around the circuit board connections. The fuse is replaced and the thermostat begins to operate properly. To verify the results, you cycle it twice in the heating and cooling modes. You ask the customer for the instructions and proceed to program the thermo­ stat to the customer-desired temperature settings. Once you've finished your work, you review the program­ ming and operation with the homeowner. The owner is presented with the invoice, which is explained to the customer's satisfaction. Unfortunately, many customers think it is easy to change out a thermostat. In this case, the homeowner most likely shorted two wires together and blew the circuit board fuse. However, the blown fuse saved the transformer.

SUMMARY

Figure 11-38 Mercury thermostat recycling bin found in s� me

air conditioning supply houses. Mercury recovery and recycling are important to reduce landfill and water supply contamination by this mineral.

SERVICE TICKET Your third service call of the day takes you to a customer who purchased a programmable thermostat with the idea of saving money. The customer replaced an old-style me­ chanical thermostat with this new one. After wiring the thermostat, the system did not work. There is a visual dis­ play on the face of the thermostat. The flashing battery icon on the thermostat face indicates that this control is operat­ ing solely on battery backup. There are three AA alkaline batteries located in the back of the thermostat. Where do you start? Think about it for a minute before you proceed. Removing the thermostat from the wall base, you notice that all of the wires are in their correct position. The R was connected to the R terminal, the Y to the Y terminal, etc. There is no voltage measurement between R and c. There should be 24 volts feeding power to the thermostat and measured between R and C. Where is the 24-V control source? The common control voltage (24 V) is found in the air handler or furnace. You locate the furnace, remove the furnace door, and notice a circuit board. A close look at

A thennostat is 1nerely a s·witch that auto1natically controls a heating, cooling, or refrigeration system. The modern dig­ ital thermostat is more accurate, easier to read, and controls the setpoint temperature more closely than do the old-style mechanical thermostats. Some 1nodels are programn1able. To save energy, the contractor or homeo,vner can set times of the day when the equip1nent can be ttu-ned up or do,vn. Some digital thermostats actually notify the user that there is a system problem. The thern1ostat can notify a cus­ tomer or their contractor by phone or via the Internet. The thermostat can trans1nit a fault indicator so that the techni­ cian will have an easier time finding the problem. The co1nmon thern1ostat tenninals are R, Y, W, and G. The C or common terminal is found on so1ne thermostats. The R terminal is a red ,vi.re and is the po,ver fron1 one side of the transformer. The Y terminal is yellov.1 and sends po,ver to the cooling contactor coil. The W tenninal is ,vhite and sends power to the heating control. The G terminal is green and controls the iJ1door blo,ver operation. The C terminal is the oilier side of the 24-V transformer and is required to complete the circuit for a digital thermostat or to operate heating and cooling controls. Finally, troubleshooting a thermostat is not difficult. First do a system survey using the ACT method or son1e other logical method of troubleshooting. If the solution to the problem leads back to the thermostat, remove the t'stat and, fron1 the subbase, jumper fron1 R to Y, R to W, and R to G. Think of the jumper sequence as a manual thermostat. The fan, cooling, and heating circuits should ,..,ork ,vhen jumping. The cooling, heating, and blo,ver should all ,..,ork. If one of the circuits checked does not ,vork, the problem is that specific thermostat v.1ire or that specific control.

THERMOSTATS

REVIEW QUESTIONS 1. What do the R, Y, W, and G terminals control on a thermostat?

191

19. vVhat programmable thennostat would be selected for a busi­ ness that has a varied schedule every day of the week and on weekends?

20. \.Yhy is it important to properly phase a transformer?

2. A heat pun1p thermostat has a B and O terminal. The O ter1ninal is wired and the B terminal is not wired. Is the reversing valve energized in the cooling mode?

21. \\That improvement is obtained by phasing two transformers together to create a 24-V output?

3. \Vhat is the purpose of the cooling anticipator?

22. vVhat is the purpose of a dum1ny thermostat?

4. \Vhat is the purpose of the heating anticipator?

23. Refer to Figure 11-39. Select the best answer. The thermostat in this drawing is a:

5. What is the purpose of a humidifier? 6. \Vhat is the common control voltage used in most thermostats?

a. cooling-only thermostat.

7. \Vhat are two advantages of a digital thermostat over a me­ chanical thern1ostat?

b. heating-only thermostat. c. heat pun1p thern1ostat.

8. \Vhat is a line voltage thermostat?

d. cooling and heating thermostat.

9. \Vhat is the mounting height of a thermostat? l 0. Should a thermostat be placed in the supply air or return air stream?

24. Refer to Figure 11-39. Select the best answer. The thermostat in this drawing has:

11. \:\That gauge wire should be used for thermostat wire?

a. a heating anticipator only.

12. The C terminal is found on what type of thermostat?

b. a cooling anticipator only.

13. How is the second stage of heating and cooling designated on a thermostat?

c. heating and cooling anticipators.

14. How do you measure a heat anticipator's low amperage using a cla1np-on ammeter?

d. no heating and cooling anticipators. 25. Refer to Figure 11-39. Select the best answer. The thennostat in this drawing has:

15. How is the cooling anticipator adjusted?

a. two thermostat wires.

16. Is the auxiliary heat in a heat pun1p thermostat energized with the Yl or \Vl?

b. three therrnostat wires. c. four therrnostat wires.

17. \:\That type of thennostat is considered a "green" thennostat?

d. five thermostat wires.

18. \Vhat is the "override" function of a programn1able the. mostat? r

e. six them1ostat wires.

FURNACE OR FANCOlL UN1T Ll 23

C

24 .--------

�

LI I.I

C

C

GROUND

SR

5

THERMOSTAT

LOGIC

Figure 11-39 use this drawing to answer Review Questions 23, 24, and 25.

UNIT 12

Pressure Switches WHAT YOU NEED TO KNOW

After studying this unit, you will be able to: 1. Install a low-pressure switch. 2. Install a high-pressure switch. 3. Install an oil pressure switch. 4. Install a fan cycling switch. s. Troubleshoot a low-pressure switch. 6. Troubleshoot a high-pressure switch. 7. Troubleshoot an oil pressure switch. 8. Troubleshoot a fan cycling switch.

Various types of pressure s,-vitches are used in air condition­ ing and refrigeration equipment. They are considered safety devices that will temporarily or permanently shut do·wn a piece of equipment should a pressure S\Vitch open. This unit discusses the 1nost common types of pressure sv-.ritches found in air conditioning and refrigeration equip­ ment. They are the: ■ ■ ■ ■

LO'\\'-pressure switch fligh-pressure s\ovitch Fan cycling switch (not a safety device)

12.1 LOW-PRESSURE SWITCHES The purpose of the lo,v-pressure s,-vi.tch (LPS) is to stop the com­ pressor \.vhen the refrigerant pressure is too lo\.v. Lo\.v refrigerant pressure reduces system capacity and reduces the amount of gas retwning to cool the motor ,vindings. The motor can overheat and trip out on its overload. Low charge also freezes over the coil, \.vhich reduces capacity and can cause liquid flooding since little heat is being transferred into the refrigerant. A frozen coil ,\rill block airfl.o\V through the air handler and duct system. The syn1bol for a low-pressure s"vitch is illustrated in Figure 12-1. The sen1icircle on the lower part of the syn1bol represents a refrigerant pressure do1ne. When the pres­ sure falls belo,-v its setpoint, the pressure in the don1e drops, ,vhich opens the s,-vitch contacts. A lovv-pressure s,,ritch can be preset to a specific pressure or the pressure setting can be adjustable. Figure 12-2 shows a

Oil safety switch.

This unit discusses the installation, operation, and trouble­ shooting of these control or safety devices. We sho\V how these devices fit in a ,viring diagran1 and also give tips on ho\v to test the pressure s,vitch after installation. It is not only i1nportant to know· ho\v to troubleshoot these devices, but it necessary to understand ho,,v to test and replace pressure svvitches. Generally, the t\-vo types of pressure switches are the 1nechanical type or transducer type. A mechanical pressure switch relies on a flexible diaphragm that causes a set of con­ tacts to open or close \vhen pressure is increased or decreased. The pressure transducer converts pressure into an ana­ log electrical signal. The \.Vord transducer means "to trans­ form" from one type of energy to another. Pressure applied to a pressure transducer produces a deflection of the diaphragn1, ,-vhich introduces a strain that can be detected by diaphragn1 1novement. The strain produces an electrical resistance change that is proportional to the pressure. Pressure transducers are sin1ilar to mechanical-type pressure svvitches. The major dif­ ference is that the control "riring leads back to a solid-state circuit board or other advanced control circuit. At this ti1ne, n1ost pressure transducer s,vitches are of the less expensive mechanical design type. You will, ho,-vever, 192

find pressure transducers in more sophisticated HVACR equipn1ent. For example, the electronic expansion valve (EXV) ,vill most likely have pressure transducers to control superheat via a data feed to a microprocessor.

Figure 12-1 This is the symbol for a low-pressure switch. The semicircle at the bottom of the symbol represents a pressure dome. As the pressure drops the linkage connected to the top of the dome drops, opening the circuit.

Figure 12-2 This preset low-pressure switch is used in air conditioning applications. The switch is screwed on to a Schrader valve fitting that is located on the compressor or suction line.

PRESSURE SWITCHES

LOW PRESSURE

preset pressure switch. Figure 12-3 shows a lo,v-pressure s·witch brazed onto a suction line. A lo\v-pressure S\vitch can also be installed on the low side fitting of a semi-hermetic compressor. v\lhen the suction pressure drops below a preset level, the low-pressure s,-vitch opens the control circuit, stopping the operation of the compressor or condensing u11it. Here are some com1non lo,v-pressure cut-out pressures for air condi­ tioning applications: ■ R-22 = 20 to 25 psi ■ R-410A = 60 psi.

The cut-in or closing pressure is 20 psi higher than the cut­ out pressure. The closing pressure for R-22 ,vould be 40 to 45 psi. The dosing pressure for R-410A ,vould be 80 psi. The cut-in and cut-out pressures vary by equipment manufac­ turer, but these pressures are reasonable for air conditioning

193

Figure 12-3 A preset low-pressure switch is

brazed onto the suction line of this condensing unit. A high-pressure switch is below it, brazed to the discharge line.

systems. Refrigeration applications operate at lo\.ver pres­ sures than air conditioning units. The lo,v-pressure cut-out setting for refrigeration applications is 0 psi or in a vacuum measured with inches of mercury (Hg). Figure 12-4 sho,-vs an adjustable lo,v-pressure switch. The advantage of this s,-vitch is that it can be used ,vith a range of different refrigerants and applications. Another advantage of the adjustable lo,v-pressure s,-vitch is the operating ainper­ age. The adjustable low-pressure s,vitch handles higher start­ ing and running amps ,vhen compared to the preset s\.vitches. In son1e sn1aller condensing units, the compressor amperage runs through the lo,-v-pressure s,vitch. Adjusting this loiv-pressure s,vitch is easy. Set the de­ sired cut-out and cut-in pressures. Some other models are more difficult to set up. Let's look at an ex.ample using this type of low-pressure s,vitch.

Figure 12-4 This adjustable low-pressure switch

has cut-out and cut-in settings that should be adjusted to the refrigerant type and application. The low-pressure capillary line comes from the bottom of the pressure switch and is attached to the suction side of the compressor. The cap tube is protected with a plastic cover to shield it from possible damage and vibration wear, which could create a leak.

194

UNIT 12 Figure 12-5 View of a low-pressure switch

WIRE CONNECTIONS

EXAMPLE 12.1 SETTING A LOW-PRESSURE SWITCH Use Figure 1.2-5 for this example. Vv'hat are the low-pressure cut­ out and cut-in pressures?

SOLUTION Let's review the settings so that you can use this information to set an adjustable low-pressure switch. Setting this low-pressure switch is easy. Subtract the cut-out pressure from the cut-in pressure. Son1e low-pressure switches have a different �ray to set up the cut-out and cut-in pressures. In this case the cut-out is about 80 psi and the cut­ in is 100 ± 5 psi. If the operating low side pressure drops below 80 psi, the control circuit will open. vVhen the pressure r.ises to 100 psi, the low-pressure switch will dose and the compressor will begin to operate. Depending on how the syste1n is wired, the compressor will cut off and the condenser fan 1nay or may not cut out.

EXAMPLE 12.2 SETTING A MORE COMPLEX LOW-PRESSURE SWITCH Here is a different exan1ple of a low-pressure setup that requires n1ore thought. Figure 12-6 shows one type of low-pressure switch that you 1nay encounter. Adjusting this type of low-pressure switch can be a little confusing. The low-pressure switch will state so1nething like tl1e follow­ ing inforn1ation on the cover: Cut-out

=

with the cover removed. The switch is set to open at 80 psi and close at 1 oo psi. These are approximate settings and must be checked prior to installing the switch on the system. The pressure cut-out and cut-in may be off ±5 psi or more. The wire connections are the two screws on the right side of the switch.

Cut-oul

= =

Cut-out

=

Cut-out

Cut-in - differential 100 psi - 75 psi 25 psi

The low-pressure switch will open the circuit at 25 psi. The low­ pressure switch will close when the pressure rises to 100 psi. This pressure switch can be used for a variety of refrigerant pressures. You will need to know the recon1mended cut-out.

t

100

Ml

-

35 400

-

f CUT IN CUT OUTIS , CUTIN..:........r LESS OIFFEROOW.

°l,IUI

cut-in - differential

This formula can be stated in another way. For example, you could say: Pressure switch opening pressure = Closing pressure n1inus the pressure differential between opening and closing the contacts

I

For this exrunple we notice that the low-pressure switch set­ tings in Figure 12-6 are set as follows: ■ Cut-in pressure of 100 psi (right side) ■ Differential of75 psi (left side).

SOLUTION Let's plug this information into the formula. Adjust the pressure cut-in to read 100 psi. Adjust the differential pressure to read 75 psi.

Figure 12-6 This type of low-pressure switch requires a minor

calculation to find the pressure cut-out.

PRESSURE SWITCHES This is just an example-it is not intended for any specific refrigerant type or operating system. Looking at the range of pressure settings, this pressure switch could also be used as a fan cycling s·witch (discussed later in this unit). The lo\v-pressure s,vitch in Figure 12-6 vvill need to be brazed or flared into the suction side of the system. When brazing, best practices require a suction line ,vith a nitrogen purge to prevent carbon conta1nination in the refrigerant lines.

12.2 LOW-PRESSURE SWITCH INSTALLATION Most replacement lovv-pressure sv.1itches are good from the factory. Ho,vever, if desired, a sv,itch can be quickly checked prior to installation. Here are two steps that will save you extra work and confusion if a svvitch does happen to be defective: 1. The pressure svvitch will be open or have an infinite resistance reading before attaching it to a test pressure. Check it for an infinite resistance reading. 2. Next, hook the ohm1neter to the low-pressure sv.1itch leads and pressurize the switch ,vith nitrogen or some other inert gas. The lovv-pressure S\----1 4

r··--,·· .. ·----------I '

'

OlL PRESSURE DIFFERENTIAL S\VlTCH

-··-··-··-··-··-··-··_J

Figure 12-32 Power continues from timer TMR1 to@, L, and Mand on to the right side of the diagram.

O The@ coil controls two sets of contacts. It will close

C\.VFS

------U-o------0-­

7

7

the CR1-NO contacts at the bottom of line 7, under the CWFS, as shown in Figure 12-33. The@ coil will open the liquid line solenoid valve.

sHowN WITH NO CHILL \.\/ATER FLOW

1----f

CRl-NO 6

K@)----@}t Ct)

Figure 12-33 The CR1-NO contacts will close when the@

coil is energized.

O The second pair of CR1-NO contacts between termi­

nals 7 and 11 is also closed. See Figure 12-34. These closed contacts will energize coil®·

O The sc1 contacts in the red oval will close, operating compressor #1 or�, as shown in Figure 12-35.

Note: If the oil pressure differential is not adequate, the OFS1 heater will cause the normally closed L and M con­ tacts to open, thus stopping the control voltage to chiller compressor #1 (COMP-1).

CRl-NO

CISS

L-

..__�

.

S(?fT-ST� TER_-:_rEIUv�ALS __J _.

Figure 12-34 The CR1-NO contacts will close, energizing the§ coil.

(continued)

210

UNIT 12

• --•

000 AWG

CBl

ClSS

000 A\VG

-------------0.,,-----;, - ----------Q-\...1>...A.J

·---------'

200A

Figure 12-35 The three-pole contactor

-------------0'-_s

COMP-I 50HP 150 FLA

sc1 closes, providing power to the compressor.

DEPRESSOR PIN I

I

Figure 12-36 A depressor pin is found in the head of some flare fittings.

TECH TIP Figure 12-36 shows the depressor pin found in the head of some flare fittings. The pin is important if a Schrader valve fitting is used. Not all refrigerant fittings have a valve and not all safety switches have a depressor pin.

SERVICE TICKET Day 1: In the spring you are asked to respond to a "no cooling" call at a recreation center. When you arrive at the job site, the manager tells you that this is the first time air conditioning has been needed since early

November. The building is about 80° F and uncomfort­ able because of the high humidity condition. The man­ ager states that she turned on the air conditioning about 3 hours earlier and the temperature has continued to rise. It is especially warm in the office, which has three employees, three computers, a large copy machine, a coffee bar, and an operating television set. Beginning the ACT method of troubleshooting, you notice that the 10-ton semi-hermetic compressor is not operating. The manifold gauge and clamp-on ammeter are hooked up to the condensing unit. The pressures on the high and low sides of the R-410A system are equal­ ized close to 240 psi for each side. After more inspection you notice that the oil safety pressure reset button is pushed out. You push the reset button and the compres­ sor begins to operate. Next, you notice the following: ■ The 12-amp draw on the compressor is below the 15 RLA amps. ■ The head and suction pressures are falling in line for an R-410A system. ■ After 10 minutes of run time, the supply air is 60° F. ■ The air filter, evaporator coil, and condenser coil look clean. • The net oil pressure is 25 psi and, after running, the oil level looks good for that model of compres­ sor. The oil level was checked prior to starting the compressor. Everything seems to be okay except for the oil safety trip. You ask the manager if she wants a spring clean and check. She tells you that service is scheduled for next week. Since you were not able to find the problem, the dispatcher told you to suspend any charges, but write up

PRESSURE SWITCHES

a service ticket documenting the reading and problems. It is difficult to charge a regular customer when a prob­ lem has not been solved. You explain the "no charge" invoice to the manager and she signs and returns it. Is there anything else that should have been checked? Day 2: The service manager asks you to come to the office prior to your first service call, which you notice is the recreation center again. It is another "no cooling" call. After a discussion with the service manager, you are planning a different approach to solving the problem. When you arrive on the job, the manager says it is not cooling again. After the routing inspection, you no­ tice that the oil safety switch is tripped again. This time you hook up a suction pressure gauge to the oil pump's Schrader valve, the suction side, and discharge side before hitting the reset button. This requires two sets of manifold gauges: two compound gauges to measure oil pressure and suction pressure. Only one gauge is re­ quired to measure the high side pressure. The clamp-on ammeter is hooked up. The oil level in the compressor sight glass is higher than yesterday. The compressor is not yet running. The reset button is pushed and the compressor begins to operate immediately. The oil level in the sight glass begins to drop. The suction pressure drops and stabilizes at 188 psi (40° F). The oil pressure fluctuates between 190 and 196 psi. The compressor sight glass has oil foaming and seems to drop to a normal level after a minute or two of operation. After 120 seconds of operation, the compressor shuts down. The oil safety switch is pushed out again. It is definitely a refrigerant dilution problem since the net oil pressure differential was not developed. At least 9-psi differential is required to keep the system running after 120 seconds. What do you do next? If the reset button is pushed again it may work as it did yesterday. In the meeting with the service manager, he asked you to check the following: 1.

Inspect the crankcase heater. The crankcase

heater is not warm. Taking an amperage measure­ ment reveals no amp draw. The heater will need to be replaced. 2. Inspect the suction line for refrigerant traps. The suction line does a loop over the evaporator and drains directly into the suction side of the compres­ sor. No trap in this design. Looping the suction line higher than the evaporator coils prevents liquid refrigerant from draining the evaporator into the compressor during the off cycle. Good design. 3. Check the oil level. The high oil level noticed prior to starting the compressor could be a result of liquid refrigerant condensing in the crankcase when it gets cool at night. During the night, the unit is off until the manager arrives in the morning. Foaming is a sign of liquid refrigerant boiling in the crankcase.

211

The solution is to replace the open crankcase heater. The compressor may come back on if the oil safety reset button is pushed a second time. Instead of taking the risk of a second oil failure, you turn your heat gun on and direct it toward the crankcase of the com­ pressor. The next step is to go to the supply house and pick up the replacement crankcase while the refrigerant is warming and boiling to a vapor. You return and install the crankcase heater. The crankcase heater is energized and draws a couple of amps. It begins to feel hot to the touch. The reset button is pushed and the oil pressure differential after 120 seconds of operation is now 40 psi. This will keep the compressor operating. You complete the invoice and discuss the work with the recreation center manager. Your service manager calls the customer in the morning and she says that the system is cooling. Some­ times oil safety problems take a couple of trips to solve, especially if the reset button is pushed without hav­ ing your gauges hooked up to measure oil pump and suction pressure differentials. This problem could have been solved on the first trip with a little more observa­ tion and by checking the common causes of oil pressure problems. Lesson learned.

SUMMARY This unit discussed so1ne of the comn1on pressure sv.ritches used in air conditioning and refrigeration equipn1ent. Other types of pressure s.vitches are also used in various heating, air conditioning, and refrigeration applications. The lo,-v-pressure sv1itch is used to temporarily break po,ver to a circuit ,vhen the suction drops belo,-v a preset level. Low refrigerant pressure •..vill cause a co1npressor motor to overheat, since the volume of the cool gases is reduced. Low refrigerant can also cause the evaporator coil to freeze up, thus reducing heat transfer and airflo,v. The ice layer can becon1e several inches thick and .vill need to be tha,,ved prior to operating the system again. The high-pressure s,vitch is used to temporarily or per1nanently stop the operation of a con1pressor. The temporary open circuit is called an automatic reset, ·which means that the high-pressure s.vitch ,,vill close ,vhen the pressure drops to a preset level. The high-pressure s,vitch with a manual reset ,-vill require the tech to push a button on the s,vitch that closes the contacts and restarts the con1pressor. It is impor­ tant for the compressor to be protected from high-pressure and overheating conditions. These conditions .vill severely damage the compressor if it is left to operate in this high­ pressure condition. The fan cycling s,vitch is used to turn off the condenser fan ,vhen the head pressure drops too low to effectively push

212

UNIT 12

liquid refrigerant through the metering device. Most 1neter­ ing devices require a 100-psi pressure differential bet\.veen the high side and lo,"' side in order to achieve the required refrigerant flo,v rate to cool properly. The oil pressure safety s,vitch keeps the compressor from being damaged due to a lack of lubrication. The oil safety s,"1'itch operates on a pressure differential. This is called net oil pressure. The oil safety svvitch operates on the pressure difference between the suction pressure and oil pump pres­ sure. Before the compressor starts, the suction pressure and oil pump pressure are the sa1ne. As the co1npressor starts, the suction pressure drops and the oil pump pressure increases. The oil safety s,-vitch 1nust develop at least a 9-psi differen­ tial in 120 seconds of running time. If the differential is not developed in the allotted time, the oil safety s,"1'itch vvill open the control circuit and stop the compressor. This unit also discussed the installation and troubleshoot­ ing process required of these pressure s,,1,'.itches. It is in1portant to check the "failure" mode operation of the s·witch ,vhen it is replaced. The replacen1ent installation will require that the switch be checked to ensure it has been ·wired correctly. It is a "best practice" to check any replacement part under the conditions in '"'hi.ch it ""ill be operating. If it is a safety device, it should be tested under the conditions it ,vas designed to protect against; for exan1ple, you could cre­ ate a low-pressure condition to see if the lo\v pressure stops the compressor when the suction pressure drops belo\v its setpoint.

REVIEW QUESTIONS I. V{hat is the purpose of a low-pressure switch? 2. vVhat is the purpose of a high-pressure switch? 3. What is the purpose of a fan cycling switch? 4. vVhat is the purpose of an oil pressure safety switch?

5. vVhat would cause a low-pressttre switch to trip? 6. \A/hat would cause a high-pressure switch to trip? 7. \i\'hen would you expect to see a fan cycling switch stopping a fan? 8. \'\'hat are two reasons an oil safety switch will open? 9. How do you test a replaced low-pressure switch? IO. How do you test a replaced high-pressure switch? 1 I. Vv'hat are the two refrigerant connections for an oil pressure safety switch? 12. How do you test a fan cycling control? 13. \\.'hat are the low-pressure settings for a system with anR-22? AnR-410A? 14. vVhat are the high-pressure settings for a system with anR-22? AnR-410A? 15. Here are readings from gauges connected to a c01npressor that is using anR-410A: ■ Suction side: 90 psi ■ Head pressure: 385 psi ■ Oil pump pressure: 9 psi. \'\'hat is the net oil pressure? 16. \·\'hy is it i1nportant to have a working crankcase heater? 17. List six reasons why an oil safety switch will open the control circuit to the compressor. 18. Refer to Electrical Diagram ED-3. If OFSl opens due to inad­ equate oil pressure, will COMP-2 continue to operate? 19. \,Vhat is the safety device shown i11 Figure 12-37? 20. Does the safety device in Figure 12-37 have a fixed or adjust­ able setting? 21. Refer to Figure I 2-38. \'\There are the capiUary lines connected in the refrigeration systen1? 22. Refer to Figure 12-39 or Electrical Diagram ED-2. Does this diagram have a low-pressure switch? High-pressure switch? Oil safety switch? 23. Refer to Figure 12-39. If a safety device opens, will the evapora­ tor fan continue to operate?

OIL FAILURE CUTOUT

Figure 12-37 use this image to answer Review Questions 19

and 20.

Figure 12-38 use this image to answer Review Question 21.

PRESSURE SWITCHES

C o--o-iJ-o------.--+---+----0

COI\1PRESSOR #1 FLA 8.5 A

.--ir--� o--o-iJ-o------

.,___� 0--o-tJ-o-------

LEGEND

---o--1 E-o

EF .-t--t---OO---tf-o-------

... ¥/Ir-.

w F1 )

•-�• - I I I I

PANEL '+--------42

Rl

I I I I I

----}--11--�----I

13

EF

1RCTSTATI

1 I

I I

.., _____ _J

14

4

Rl

6

7 LP

DTS

TS

TD

1(5MIN)2 1 7

6 . ��-a-.-o-®·T·®·T-� 3

C

14

1 1--+--------42 8 95

213

96

---t19t- CON T F RATlNG CL TYl'E lNPUT VOLTS J 15 VAC 13.1 FULL LOAD INPU T AMPS ENERGY SAVING DESIGN

0 1

3

l 1720 B 60

(Q)lO

ULTRA POWER SERIES l\.1ODEL NO. TB0014DFA VOLTS208-230/460 ANIP. 3.8-3.6/1.8 / ODP ENCL. FRAlvIE NO. 143T' 'tvJAX. AMB. 40 oc SERV ICE FACTOR 1.15 TIME RATIN G CONT. BRG. D.E. 6205ZZ KVA CODE NO. O.D.E. 6205ZZ K NElvtA DESIGN B NElvIA F.L. F.FF. 77 DATE CODE SER# 0016874!1� 0396

TATUNG CO.

Figure 14-12 This is the nameplate for a variable-speed motor or variable­ horsepower motor.

07

3 PHASE INDUCTION MOTOR

✓

- HP • RPM INS. HZ

4

l'LANTM t::54�25 MADE IN U.S.,\.

C E ELECTiliC INDUSTRIAL CO.l\1:PANY l -� RELIAN 602095-71-A CLEVELAND, OHIO44117

2

5

�; �i �;

CONNECTIONS

LOW VOLTS

41 7 51 8 961 I' 2, 3,

HlGHVOLTS

MADE 1N TAIWAN R.O.C. 4-20706

4

0

.,

-1

Figure 14-13 This nameplate has information on how to wire a low­ voltage or high-voltage connection. The horsepower and speed are set.

238

UNIT 14

Model and Serial Number Each motor ·will have a model number and may have a serial number. This information ·will be useful if the n1otor needs to be replaced. This information ,.vill allo,-v you to choose an exact replace1nent or select a substitute 1notor. A sample of a model number is indicated by the nu1nber 1 in Figure 14-13.

TECH TIP Will a 230-volt motor run on 208 volts? The motor is al­ lowed to operate at +10% of the nameplate voltage. In this case, the performance will be reduced by 10% to 12%. The motor will run at a higher temperature. In this case, there will be no undervoltage reserve.

14.9 RATED VOLTAGE The rated voltage is the voltage that is applied to the n1otor. The rated voltage is + l 0% of the nameplate voltage. For example, a voltage rated at 480 V ,vill have a + 48-V range above and belo,,v the 480 volts. Hence, in this case the operating voltage should be 432 to 528 volts. Operating outside this range ·will cause the motor to overheat and "trip out" its overload protection. If it is a dual-voltage 1notor, the + 10°/4 "vill apply to the lo,vest voltage and highest voltage on the dual-voltage mo­ tor. So, for a 208/240-·v motor, acceptable voltages are found by subtracting 20.8 volts from the 208-V side and adding 24 volts to the 240-V side. Therefore, the range ""ill be 187.2 volts to 264 volts. For long motor life, it is best to operate the 1notor near the voltage rating. A slightly higher voltage is best. It is almost impossible to operate on the exact design voltage such as 240 or 480 volts. Measure motor voltage un­ der a normal operating load.

TECH TIP some common colors for single-phase motor wires are: ■ White or yellow= common power wire ■ Brown or brown with a white tracer = capacitor connections ■ Black= high speed ■ Blue= medium speed ■ Red = low speed ■ Green= ground. Note that this color code is not used by all motor manufacturers and color codes from overseas manufac­ turers vary widely.

14.10 RATED LOAD AMPS (RLA) As the torque load on a motor increases, the amperage required to po,ver the motor also increases. When the rated load torque and horsepow·er are reached, ilie corresponding amperage is

kno\-vn as the rated load amperage (RLA). On a compressor 1notor the RLA condition 1na:y be reached when a fully charged air conditioning systen1 is operating at its full Btuh rating on a very hot day. When possible it is best to run the compressor below the rated load amps. The lovver the amp draw, tl1e cooler the temperature at ,vhich the motor ""ill operate. Cooler op­ eration equals longer and more efficient motor life. A blow·er 1notor or pun1p ,-vill operate at RLA ·when they are moving the designed airflo"" or liquid flo,-v. A lack of air­ flow around a fan or pump motor will cause the 1notor to overheat. This is noted by the number 3 in Figure 14-12. Fan n1otors co1nmonly use the term full load a1nps (FLA) instead of rated load amps.

14.11 LOCKED-ROTOR AMPS (LRA) Locked-rotor amps or locked-rotor current is found ,vhen a n1otor starts up in four conditions, as discussed next. When alternating current motors are started with full voltage applied, they create an inrush current that is usually many times greater than the value of the running full-load current. This very high amp condition occurs momentarily. The value of this high current can be important on some installations because it can cause a voltage drop that might affect other equipment. High inrush current can also di1n lights and affect sensitive electronic equipn1ent. The second LRA condition is found when the motor is mechanically locked up and cannot move. In this case high ainperage ""ill be dra,vn until the overload device opens the circuit to the n1otor. The third LRA condition is created when the inco1ning voltage is lovv. Finally, a LRA 1nay occur ,-vhen a start capacitor or relay is defective or ,vired up incorrectly. There are two ways to find the LRA value of the motor: I. Look it up in the motor performance data sheets a-... ',.,...... : , -"""" A TO R

---,

C --\.!:.,J--YEL

,,

7

I 'I

I

... -,

--

\.!:.) ] ��------------------ ! y

U

i

[___________ TC i THERMOSTAT

CO11PONENT ARRANGEMENT

FC

OT

0-1t-O

�®-I 'if�

GRN

COMPR Figure 15-49 This is a diagram for a three-phase, 460-V condensing unit. The compressor uses a three-phase, 460-V motor. The remaining components use a single-phase 460- or 230-V motor.

MOTOR TYPES

\

Figure 15-50 To protect a motor from rain or moisture, it is always a good practice to leave a drip loop in the lead wires so water will not be channeled directly into the motor housing. Be careful to keep the loops short enough to prevent the wires from making contact with the load.

\

\

0

275

\ \\ 0

0

FASCO

• •

15.18 MOTOR MOUNTS AND ACCESSORIES S01ne of the comn1011 111otor mounts are: ■ ■ ■ ■ ■

Rigid Cradle Belly band Stud C-frame.

Motors have several mounting accessories including resilient bases, bracket assemblies, band 1nounting kits, and adapter plates.

TECH TIP When installing a condenser fan it must be protected against rain and moisture. The wiring must also be placed so that the wire does not become a path for water flow into the motor's electrical compartment. Figure 15-50 shows an example of a drip loop used to prevent water infiltration.

15.19 MOTOR VENTILATION \'\7hen selecting a replacement motor, the ventilation pat­ ten1 of the replacement 1notor must match the original mo­ tor as closely as possible for safe and maximum motor life. Moisture and vapor exposure must be considered. Here are the common motor ventilation styles: ■ ■ ■ ■

Open, fully vented Open drip-proof Totally enclosed, nonvented Totally enclosed, fan cooled.

Open Motors or Fully ventilated Motors Open or fully ventilated motors that are protected from the ,veather and are not built into a co1nbustible structure benefit fron1 having a fully or partially ventilated fran1e. Figure 15-51 shows ventilation slots in the motor shell and end shield that cool the motor's vvindings and bearings. Heat fro1n the coils and bearings is allo,ved to dissipate into the ambient air, lo,v­ ering the temperature and max.i1nizing motor life.

276

UNIT 15

Figure 15-52 Open drip-proof motors are used in equipment where open ventilation is needed for cooling, but where the motor may be exposed to moisture drips onto the windings. Figure 15-51 Totally open ventilated motors have vent slots in the shell and end shield. These motors may be smaller than enclosed motors.

Open, fully vented 1notors are used in indoor applica­ tions that are protected from 1noisture and vapor. \,Vhen an open vented 111otor is required in equipment that is exposed to rain, snow, or other type of 1noisture, a par­ tially open motor is available ·with closed end shields -...vith the shaft up or do,vn to protect the vvindings and bearings from liquids.

Open Drip-Proof Motors The open drip-proof design sho-wn in Figure 15-52 is used where motors are exposed to the weather or where there may be a fire hazard from molten or flaming materials. The frames are typicaHy totally enclosed or drip-proof to allovv for lovver operating temperatures. The upper half of the shell is closed to prevent moisture fron1 dripping into the n1otor. These are used in shaft horizontal installations only.

Totally Enclosed Nonvented (TENV) Motor The totally enclosed nonvented motor has no vent openings ( see Figure 15-53). It is designed for maximum protection

from vveather and contaminants. The TEN\T 1notor 1nay have the shaft installed in any direction. These motors run hotter than open-type motors, therefore they should never be used to replace an open vented 1notor.

Totally Enclosed Fan-Cooled (TEFC) Motor Totally enclosed fan-cooled motors have no opening in the shell or end shields. Coo.ling is accomplished by an exter­ nal fan system to 1nove the air over the motor shell and end shields. These motors are used in equipment ,vhere no cool­ ing air is provided by the load. Figure 15-54 sho,,vs a TEFC motor.

15.20 MOTOR REPLACEMENT AND AMP RATINGS One ,,vay to ensure that a replacen1ent motor,vith sin1ilar out­ put is chosen (,vhen the horsepo\ver is unknovm) is to select a n1otor \vith a current rating that is very similar to that of the failed motor. Nlotors of the same type, current, and volt­ age ratings, and stack length will likely have very si1nilar out­ put. Table 15-2 ,vill help the technician choose a replacement

MOTOR TYPES Table 15-2 Amp Ratings for use When Choosing a Replacement Motor

cn±lll«@D

Figure 15-53 The totally enclosed, nonvented (TENV) motor

has no shell ventilation openings.

Figure 15-54 The totally enclosed fan-cooled (TEFC) motor

does not have any vent openings in the shell or end brackets. The motor has an internal fan that moves air over the motor shell and end shields.

Nameplate Amps of the Defective Motor

Nameplate Amp Range of an Acceptable Replacement

1.0

1.0-1.25

1.1

1.1-1.37

1.2

1.2-1.52

1.3

1.3-1.62

1.4

1.4-1.75

1.5

1.5-1.87

1.6

1.6-2.0

1.7

1.7-2.13

1.9

1.9-2.37

2.0

2.0-2.5

2.2

2.2-2.75

2.4

2.4-3.0

2.6

2.6-3.25

2.8

2.8-3.5

3.0

3.0-3.75

3.3

3.3-4.12

3.6

3.6-4.5

4.0

4.0-5.0

4.4

4.4-5.5

4.8

4.8-6.0

5.0

5.0-6.25

5.5

5.5-6.87

6.0

6.0-7.5

6.5

6.5-8.12

7.0

7.0-8.75

7.5

7.5-9.37

8.0

8.0-10.0

8.5

8.5-10.62

9.0

9.0-11.25

9.5

9.5-11.87

10.0

10.0-12.5

10.5

10.5-13.12

11.0

11.0-13.75

11.5

11.5-14.4

12.0

12.0-15.0

(Courtesy Regal Beloit.)

277

278

UNIT 15

motor if the amperage of the defective 1notor is knov\rn. The current rating of the replacement motor should be the san1e or no 1nore than 25% greater than that of the 1notor being replaced. One of the steps to insure a replacement motor ,vith similar output is selected (when the .HP is unknovvn) is se­ lecting a motor ·with a current rating very sin1ilar to that of the failed 1notor. Motors of the same type, current and voltage ratings and stack length, \\rill likely have very similar output. A replacement n1otor should be selected ,vith a current rating the same and not more than 25% greater than the de­ fective motor.

TECH TIP some motors bearings are sealed, while others re­ quire periodic lubrication. The lubrication may be in the form of a light, nondetergent oil or grease. Use the manufacturer's recommendations for type and frequency of lubrication. overlubrication may damage the motor.

15.21 MOTOR ROTATION 1vlotor rotation in n1ost cases is in1portant. For many com­ pressors, the direction of rotation does not n1atter. This 1neans that if the con1pressor is ·wi' red correctly it \Vill turn in the right direction to create compression and pu1nping action toward the discharge line. Some three-phase compres­ sors require a specific rotation or the oil pump w'ill not create the needed oil pressure. Many replace1nent single-phase fractional horsepower n1otors used in condensing units or air handlers have direc­ tional ,viring options. Single-phase 1notors that do not have this option may have one of the fol10¼1ing abbreviations on the nameplate: ■ ■ ■ ■

CCLE ( counterclock\vise lead end) CCSE ( counterclock\vise shaft end) CWLE ( clockwise lead end) CWSE ( clock\vise shaft end)

This "'1ill tell you the shaft rotation and the rotation orientation. For exan1ple, if the nameplate bas the abbre­ viations CWSE, it means that ,vhen looking at the shaft end (SE), the n1otor ,.vill turn in a clockvvise direction (CW). CWLE refers to vie,ving the 1notor from the lead end (LE), or looking at the n1otor ,vhere the ,vires enter it. In this vie¼', the 1notor \\rill turn in a clock,vi.se direction (CW).

SERVICE TICKET You are troubleshooting a residential 4-ton air condition­ ing unit. At the beginning of the troubleshooting process, you do all the quick checks using the ACT method. Air is flowing from the indoor registers and the condensing unit. The thermostat has been switched to cooling and the set­ ting is low enough to energize the condensing unit. After hooking up the clamp-on ammeter and manifold gauge set, you notice there is no amperage on the compressor and the high and low pressures are equalized. What does this mean? The compressor is not operating! A minute later the compressor groans, draws locked rotor amps, and shuts off again. What is the problem? The problem seems to be the compressor or the compressor circuit. You check the start and run wind­ ings from the contactor wire and run capacitor termi­ nals. They measure 15 and 5 ohms, respectively, which seems to be good. The resistance reading from the compressor to ground was infinity or OL on the digital meter reading. The electrical features of the compressor are good. The compressor could be mechanically locked. Next, check the electrical components. The com­ pressor motor is CSCR. A visual inspection reveals that the capacitors and potential appear to be in good shape. The run and start capacitors check out within their mi­ crofarad rating. The potential relay coil measures 5.1 kn. Potential relay coils measure high resistance, starting around 4 kn and going as high as 8 kn. The potential relay contacts measure infinity. The potential relay con­ tacts, terminals 2 and 1, should measure near o n. You have found the problem. Without the normally closed (NC) potential relay contacts, the start capacitor was not in the starting circuit. The compressor would draw LRA on start-up and the compressor would open the com­ pressor internal overload. This can also be checked with a clamp-on ammeter. Place the clamp-on ammeter over the wire that is in line with the potential relay 2 and 1 terminals. When the motor starts there will be an amperage spike for a split second until the NC contacts open. If the contacts are open or the start capacitor is defective, there will be no amp spike. The solution to the problem is to replace the potential relay with an exact replacement. Test the system by start­ ing the compressor while monitoring the amperage on the common winding of the compressor and gauge pressures.

SUMMARY This unit has provided you ,,vith much inforn1ation about motors. Table 15-3 provides a summary of the n1otors dis­ cussed. It includes the motor type, starting torque, running

MOTOR TYPES

efficiency, operating cost, and usual applications. This 1notor comparison table ,vill help you revie,v and contrast the motors discussed in this unit. Finally, use Table 15-4 to aid in troubleshooting motor problems. Son1e of the conditions listed in the table were

279

covered in this unit. This table "'rill give you more ideas on ,,vhat needs to be checked to solve problems. You will notice in the table that some of the problems are electrical and mechanical.

Table 15-3 Motor comparison Chart Motor Type

Starting Torque

Running Efficiency

Operating cost

Applications

Shaded pole

Low

Poor

Low

Small fans and pumps

Split-phase

Moderate

Poor

Moderate

Pumps and fans

Capacitor start/induction run (CSIR)

High

Poor

Moderate

Pumps and fans

Permanent split capacitor (PSC)

Medium

Good

Moderate

Single-phase motors, compressors, and fans

Capacitor start/capacitor run (CSCR)

High

Good

Moderate

Single-phase motors, compressors

Three-phase

High

High

High

Commercial and industrial uses

(Source Motor Comparison Table 05-03-06.J

Table 15-4 Motor Troubleshooting Chart This table offers electrical and mechanical suggestions for solving motor problems.

Your motor service and any troubleshooting must be handled by qualified persons who have proper tools and equipment. Trouble

cause

What to Do

Motor fails to start

Blow fuses

Replace fuses with proper type and rating

Overload trips

Check and reset overload in starter.

Improper power supply

Check to see that power supplied agrees with motor nameplate and load factor.

Improper line connections

Check connections with diagram supplied with motor.

Open circuit in winding or control switch

Indicated by humming sound when switch is closed. Check for loose wiring connections. Also see that all control contacts are closing.

Mechanical failure

Check to see if motor and drive turn freely. Check bearings and lubrication.

Short-circuited stator

Indicated by blown fuses. Motor must be rewound.

Poor stator coil connection

Remove end bells, locate with test lamp.

Rotor defective

Look for broken bars or end rings.

Motor may be overloaded

Reduce load.

(continued)

280

UNIT 15

Table 15-4 (continued) Trouble

cause

What to Do

Motor stalls

one phase may be open

Check lines for open phase.

wrong application

Change type or size. consult manufacturer.

overload

Reduce load.

Low voltage

See that nameplate voltage is maintained. Check connection.

Open circuit

Fuses blown, check overload relay, stator and pushbuttons.

Motor runs and then dies down

Power failure

Check for loose connections to line, to fuses and to control.

Motor does not come up to speed

Not applied properly

Consult supplier for proper type.

Voltage too low at motor terminals because of line drop

Use higher voltage on transformer terminals or reduce load. Check connections. Check conductors for proper size.

Starting load too high

Check load motor is supposed to carry at start.

Broken rotor bars or loose rotor

Look for cracks near the rings. A new rotor may be required as repairs are usually temporary.

Open primary circuit

Locate fault with testing device and repair.

Excessive load

Reduce load.

Low voltage during start

Check for high resistance. Adequate wire size.

Defective squirrel cage rotor

Replace with new rotor.

Applied voltage too low

Get power company to increase power tap.

Wrong rotation

Wrong sequence of phases

Reverse connections at motor or at switchboard.

Motor overheats while running under load

overload

Reduce load.

Frame or bracket vents may be clogged with dirt and prevent proper ventilation of motor.

open vent holes and check for a continuous stream of air from the motor.

Motor may have one phase open

Check to make sure that all leads are well connected.

Grounded coil

Locate and repair.

unbalanced terminal voltage

Check for faulty leads, connections and transformers.

Motor misaligned

Realign.

weak support

Strengthen base

coupling out of balance

Balance coupling.

Driven equipment unbalanced

Rebalance driven equipment.

Defective bearings

Replace bearing.

Bearings not in line

Line up properly.

Balancing weights shifted

Rebalance motor.

Polyphase motor running single phase

Check for open circuit.

Excessive end play

Adjust bearing or add shim.

Motor takes too long to accelerate and/or draws high amp

Motor vibrates

MOTOR TYPES

281

Table 15-4 (continued) Trouble

cause

What to Do

unbalanced line current on polyphase motors during normal operation

unequal terminal volts

Check leads and connections.

Single phase operation

Check for open contacts.

Unbalanced voltage

Correct unbalanced power supply.

Fan rubbing air shield

Remove interference.

Fan striking insulation

Clear fan.

Loose on bedplate

Tighten holding bolts.

Airgap not uniform

Check and correct bracket fits or bearing.

Rotor unbalance

Rebalance.

Bent or sprung shaft

Straighten or replace shaft.

Excessive belt pull

Decrease belt tension.

Pulleys too far away

Move pulley closer to motor bearing.

Pulley diameter too small

use larger pulleys.

Misalignment

Correct by realignment of drive.

Insufficient grease

Maintain proper quantity of grease in bearing.

Deterioration of grease or lubricant contaminated

Remove old grease, wash bearings thoroughly in kerosene and replace with new grease.

Excess lubricant

Reduce quantity of grease, bearing should not be more than 1/2 filled.

Overloaded bearing

Check alignment, side and end thrust.

Broken ball or rough races

Replace bearing, first clean housing thoroughly.

Scraping noise

Noisy operation Hot bearings general

Hot bearings ball

(Courtesy Regal Beloit.)

REVIEW QUESTIONS I. ,.\,'hat con1ponents should be changed out when replacing a CSCR motor with an electrical burnout? 2. v\That are the advantages of a three-phase motor over a single­ phase motor? 3. '-Vhat is a split-phase 1notor?

4. Which has n1ore resistance, the start winding or the run winding? 5. '-Vhich single-phase rnotor has the best starting torque and running efficiency? 6. Of all motor types discussed in this unit, which has the best

starting torque and best running efficiency? 7. \Vb.at are three ways to troubleshoot a shaded pole motor? 8.

\-Vhat are four ways to troubleshoot a pennanent split capaci­ tor motor?

9. \Vhat are six

,,vays

to troubleshoot a CSCR motor?

10. What components make up a hard start kit?

11. You find a defective 55-mfd run capacitor on a co1npressor. You have a 40- and a 75-mfd capacitor in the service van. ls one of these capacitors an adequate replacement for the defective cap? Explain.

12. You are going to replace a CSCR co1npressor. Are there any electrical components that must also be replaced? If so, what are they? 13. Summarize the 11 points that you ·will need to know when selecting a replacement for a motor that does not have a name­ plate. 14. \Nhat resistance scale is used when checking motor windings? 15. What resistance scale is used when checking the n1otor to ground?

16. \Nhat single-phase motor would you select if starting torque or running efficiency is not a concen1? 17. What single-phase motor would you select if starting torque is not a concern, but running efficiency is? 18. \Nhich single-phase n1otor(s) have good starting torque? 19. When a motor is operating, is the coil voltage on a potential relay lower, the san1e as, or higher than the applied voltage?

UNIT 15

282 L1

L2

-------------230-1-60----------� SR

SC

cc

C

C

CH COMP CR Fl\1 FS GV HPS HR HS IFl\11 IFR LPS LS OL PS RC SC SR T,

RC

COtvIPR

CONDENSING UNIT

HR

HR

HPS

B

CR CR

AHA C CAP

Tz

T3 T4 TI\.1

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COOL

OFF t----ving the high-voltage electrical connections. The connector on the left has a black, ,vhite, and ground ,vire. If it is 120 volts, the black Vl'ire ,vill be hot and the ,vhite wire will be neutral. The green vvire is ground. The connector on the right is a 240-V motor. The black and ,.vhite V11ires ,vill both be hot. There V11ill be no neu­ tral. Ren1ove the ju1nper vvire that goes betvveen tenninals 1 and 2. Figure 16-13 is the high-voltage connector that vvould plug in to the motor. It has a black, red, and green ground ,-vire. If it is 120 volts, the black ,,vire ,vill be hot and the vvhite

290

UNIT 16

Figure 16-10 This is the module end of an ECM. The lower connector is the low-voltage single input. The upper connector with the black, white, and green wire is the continuous voltage input.

MOTOR SECTION

TECH TIP I ITCONTROL PANEL

The shaft of a de-energized ECM will not turn freely with­ out being powered up. When power is removed the shaft will have a drag or "cogging feel" from the permanent magnets that are used to make up the rotor. It will seem as if the ball bearings are worn and dragging.

16.4 INSTALLATION SETUP

Figure 16-11 The module does not need to be attached to the ECM motor body. Here a condenser fan ECM module is installed under the condensing unit control panel since there is not enough room for the full assembly if installed in one piece.

,vire ,¥ill be neutral. The green wire is ground. If it is a 240-V n1otor, the black and red ,vires will both be hot. There \\Till be no neutral. The designs of the high-voltage and lov.r -voltage connectors are different to prevent mistakes during hook­ up. These connectors are designed to come together in one ,vay, eliminating a connection error on the module. Electrical pow·er is supplied to the module at all tin1es even \vhen the motor is not running. Po,ver to the 1notor should be disconnected before re1noving the connect plugs. Plugging or unplugging the 1nodule w · ith po,ver applied may cause arching in the module. This arching 1nay dan1age the module. Also, before opening the module and separating it from the motor, allo,v 5 minutes for the large capacitors to discharge.

An air handler or furnace ,,vith an ECb-1 must be set up prior to initial operation. If the dip s,"litches on the circuit are not set up for the specific application, the motor ,vill operate at factory setting speeds that may or n1ay not be \vhat is best for the application. An ECM condenser fan does not normally need to be set up. It is progran1med and ready to operate per OEM specifications. For an air handler or furnace, it is important to first check the polarity of the 120-V po,ver supply. The hot power leg and neutral must be connected to the right places. The hot wire is "usually" black and the neutral ·white. The ground ,vire is green. To check the hot wire, 120 volts should be 1neasured from the hot ,vire to ground. If 120 volts is not measured, then you are not measuring the hot \-Vire or there is no ground or no supplied po,,,er. Next, 1neasure the neutral to ground. It should measure no voltage or 0 V. Without the proper 120-V polarity to the circuit board, the equipn1ent ,-vill not ,vork at all or it will operate erratically. \\That happens ,,vith reversed po,,ver polarity varies fron1 unit to w1it; therefore, vve cannot go over all the possible problems that can arise ·when this con­ dition occurs. There ,vill, however, be so1ne really unusual

ECM: THE GREEN MOTOR METER CONNECTED BET\.VEEN TERMINAL #4 AND #5

METER CONNECTED BET\VEEN TERJ\1INAL #4 AND #5

120

240

5

AC VOLTS

_C) •

4

'.I

2

I

00000 I

COtvt

291

AC VOLTS

_C) V

COl\,1

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ll

,,. ,,.

�

\.

VAC tvtOTORS SHOULD .,.�...:....L240 NOT HAVE A JUMPER BETWEEN

120 VAC MOTORS JvIUST HAVE AJU�1PERBEThcEN TER\\1INALS I AND 2 FOR PROPER OPERATION.

TERl\tiNALS I AND 2 TO PREVENT DA.MAGE TO THE MOTOR.

Figure 16-12 This is the high-voltage connector closest to the motor.

_f

Figure 16-13 This connector goes into the module input nearest the motor. This is a 240-V connector. The wires are color coded. Black and white or red is high voltage and green is ground.

problems. A good ground is important for all pieces of equipn1ent, \\Tith or without circuit boards. In many in­ stances it is a matter of safety to protect the technician from getting electrocuted. With 240 volts, there are two hot ,\Tires and a ground. There is no polarity issue here, but again the proper ground is extremely important. After the correct voltage and polarity have been estab­ lished, the next step is to follow the OEM setup procedures. This is often overlooked in an installation and start-up. The tech doing the install thinks that the equipment is already

set up from the factory for her specific application. For ex­ ample, the focus is usually the circuit board. A jumper ,,vire may need to be added or a jumper wire may need to be clipped under specific operating conditions. As seen back in Figure 16-2, n1any circuit boards have small dip s·witches or rotary S\Vitches that need to be set for cooling and heat­ ing operations. The user interface or thennostat may need programming. Table 16-1 is a chart from the inside door of a gas fur­ nace that lists the dip svvitch settings required for a specific ECM operation. For example, let's assume the system in­ stalled is a 3-ton unit. The tech '"'ants to set the blower for enhanced 1noisture ren1oval. He therefore selects the 350 CFJvl/ton airflo,-v row· for a 3-ton unit. Here is the setup for the dip sv.ritches: SW 1 is on. SvV 2 is off. SW 3 is off. SW 4 is on. This setting will give the 3-ton setting of 1,050 CFM when the ECM is working at 100% speed. The CFM and v,ratts of the motor can be determined if the external static pressure (ESP) is measured. ESP is a measurement of duct,-vork resistance to airflo\v. In the previous exa1nple, an external static pressure (ESP) at 0.5 for the setting described here '"'ill tell the tech that the air­ flovv is 1,000 CFM and the po\-ver consu1ned is 260 ,-vatts.

292

UNIT 16

Table 16-1 Dip Switch Settings for a Gas Furnace

This chart is found inside the door of a gas furnace. The settings must be set to operate the furnace and cooling system at the designed conditions. *UD080R9V3K Furnace Cooling Airflow (CFM) and Power (Watts) vs. External Static Pressure with Filter

-Outdoor

Unit Size

(Tons>

2.5

3.0

3.5**

-

�

-

-

EXtemal Static Pressure

Dip Switch setting

Airflow

setting

SW1

SW2

SW3

SW4

LOW (350 CFM/TON)

OFF

ON

OFF

ON

NORMAL (400 CFM/TON)

OFF

ON

OFF

HIGH (450 CFM/TON)

OFF

ON

LOW (350 CFM/TON)

ON

NORMAL (400 CFM/TON)

0.1

0..3

0.5

0.7

0.9

CFM WATTS

880 120

875 155

860 190

845 225

840 245

OFF

CFM WATTS

1020 170

1000 205

990 240

980 280

960 320

ON

OFF

CFM WATTS

1110 210

110 260

1110 320

1100 350

1100 385

OFF

OFF

ON

CFM WATTS

1040 190

1010 220

1000 260

1000 310

990 340

ON

OFF

OFF

OFF

CFM WATTS

1200 250

1200 320

1190 370

1190 415

1175 450

HJGH (450 CFM/TON)

ON

OFF

ON

OFF

CFM WATTS

1340 355

1340 425

1330 475

1320 530

1300 570

LOW (350 CFM/TON)

OFF

OFF

OFF

ON

CFM WATTS

1215 265

1210 330

1210 375

1200 430

1185 465

NORMAL** (400 CFM/TON)

OFF

OFF

OFF

OFF

CFM WATTS

1430 415

1415 457

1410 520

1385 575

1330 580

HIGH (450 CFM/TON)

OFF

OFF

ON

OFF

CFM WATTS

1430 415

1415 475

1410 520

1385 575

1330 580

NOTES: 1. *First Letter may be "A" or "T" 2. **Factory setting 3. continuous Fan setting: Heating or cooling airflow is approximately 50% of selected cooling value. 4. For Variable Speed: low speed airflows are approximately 30% of listed values. 5. LOW 350 CFM/TON is recommended for variable Speed application for comfort & Humid Climate setting; Normal is 400 CFM/TON; High 450 CFM/TON is for Dry Climate setting (Courtesy Trane Corporation.)

You ·will notice that ,-vith an ECM, the CFM stays about the same even as the airflovv becomes restricted (increased ESP). The number of ,vatts used by the motor increases as the ESP increases. Increased ,-vatts 1neans the motor is going to run hotter. This prolonged heat can shorten the n1odule's life. Again it is important to measure the external static pres­ sure (ESP) across the EC�1. The device used to measure static pressure is called a pressure differential gauge. The con1n1on brand name is made by D,-vyer Instruments and it goes by the traden1arked name of 11agnehelic. You are 1nore likely to hear the ,-vord Magnehelic rather than the correct name of pressure differential gauge. The Magnehelic measures very lo,v pressure drop, which is expressed as inches of water col­ umn and abbreviated "WC. l-lere is an example of the 1o,v

pressure differential ,ve are discussing here. One-tenth of an inch of water column (0.1) is equal to 0.04 psi. ESP in excess of 0.901'WC is usually dan1aging to the module due to excess heat. Check the manufacturer's specs to determine the maxi1num ESP. High static (restricted air­ flo,-v in the duct system) will cause the motor to operate on the high end of its design conditions, ,-vhich leads to high current dra,-v, an overheated motor n1odule, and shortened co1nponent life. Figure 16-14 sho·ws a circuit board with a green CFM light. For this model, one blink equals 100 CFM; therefore, a 10-blink sequence ,vill mean the air handler i.s 1noving 1,000 CFM (10 blinks x 100 CFM). The air handler or furnace pan­ els and ducn-vork for the unit need to be installed to obtain an accurate 1neasure1nent since ren1oving the door may allovv

ECM: THE GREEN MOTOR

CF!\1 INDICATOR

FAN SPEED DIPSWITCHE

293

There are many precautions to observe when installing equipment ,vith the ECM. It is not a "slap it in and forget it" 1notor like a single-phase n,otor.

16.5 DEHUMIDIFICATION AND ENERGY EFFICIENCY

Figure 16-14 The CFM is indicated by the green LED light.

A red

light is used to indicate power to the system. The dip switches should be set on or off using the manufacturer's airflow table.

for more airflow. This unit has a panel door with a "vie\\7 eye" to count the green blinking light indicator \Vithout ren1oving the panel. The system airflow· dip s,"''itches can be seen to the right of the CFM light. The red po\ver light is used to indicate volt­ age to the circuit board. The ECM may rock back and forth when it is first ener­ gized. The n1otor ,vill take off into the correct direction. This is normal. Install the ,viring to the condenser or air handle ECM motor so that the wire has a drip loop as illustrated in Figure 16-15. Water is the biggest reason the 1nodule sec­ tion of the motor fails. v\Tithout a drip loop the v.rater \vill track directly into the module and may damage it. When multiposition systen1s are installed, the drip loop n1ay need to be changed because the ,,viring 1nay be turned in the \Vrong position.

BACK OF MOTOR CONTROL

One purpose of the ECM design is to control the start-up and shutdo,vn of the air handler motor. The slo,�r or soft start characteristics of the ECM reduce the effects of locked rotor amp (LRA) starting, ,vhich places excess stress and heat on the 1notor 1,vindings. Another purpose of the ECM is to im­ prove moisture removal and increase motor efficiency. The indoor ECM can be progran11ned to do all of these energy saving and comfort enhancements. Figure 16-16 is a graph of the effects that result ,vhen a control circuit board is set up to dehu1nidify and save energy. The indoor fan is set to cycle with the condensing tu1it. This is usually the "Auton1atic" setting on the thermostat. Not sho1,vn in this diagran, is a tin,e delay on start-up. Som.e designs have a start and stop delay. The start delay aUo,vs the evaporator to chill for about 1 minute prior to starting the blo\ver. This graph shows that the blo,ver speed .viii slo1,vly ramp up to 50% over a period of l minute. The blo1,ver will again ramp up to run at 80% of full speed for the next 7.5 minutes. The low-speed operation allo,-vs more air contact tin1e ,vith the cold evaporator surface. !vfore contact tin1e cre­ ates more 1noisture removal, which lowers the hun,idity of the air. If the low·-speed blov.,er is operated for n1uch longer than this ti1ne per.iod, you run the risk of freezing the coil. In many instances the thennostat v.rill be satisfied when running the syste1n for this short period, less than 8.5 minutes. If the thermostat is not satisfied, the indoor m . otor speed w · ill ramp up to 100% of set speed. After the thermostat is satisfied the condensing unit shuts do,-vn and the indoor blo,ver ,viJJ slow dov.,rn operation. It v.rill continue to operate for about 3 minutes, blo,-ving air across the cold evaporator as 1,vell as n1ov­ ing the chilled air fron1 the duct syste1n. This ,-

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FACTORY PO\VER \VlRING FACTORY CONTROL \\-1RTNG FIELD CONTROL WIRING FIELD PO\VER WIRING COMPONENT CONNECTION FIELD SPLICE CONTACTOR CAPACITOR (DUAL RUN) CRANKCASE HEATER CRANKCASE HEATER S\VTTCH COMPRESSOR COMPRESSOR TIME DELAY DISCHARGE TEMP S\VITCH HIGH PRESSURE SWITCH INDOOR FAN RELAY LIQ LlNE SOLENOID VALVE LOW PRESSURE SWITCH OUTDOOR FAN MOTOR START CAPACITOR START RELAY START THERr-1ISTOR

* J\,1AY BE FACTORY INSTALLED

Figure 17-42 use this diagram to answer Review Question 28.

(Canier m#24 l bc6 Base 16, catalog #24abc6-l w) NOTES: 1. Svrnbols are electrical representation only. 2. C�mpressor and fan motor furnished with inherent thermal protection. 3. To b� wired in accordance with National Electric N.E.C. and local codes. 4. N.E.C. class 2, 24 V circuit, min. 40 VA required, 60 VA on units installed with LLS. 5. Use copper conductors only. Use conductors suitable for at least 75° C (167'"F). 6. Connection for typical cooling only lhem1ostal. for. other . arrangements see installation instructions. 7. If indoor section has a transformer with a grounded secondary, connect the grounded side to the BRN/YEL lead. 8. When start relay and start capacitor are installed start thermistor is not used. 9. CH not used on all units. IO. 1f any of the original wire, as supplied must be replaced, use the same or equivalent wire. I 1. Check all electrical connections inside control box Cor tightness. 12. Do not attempt to operate unit until service valves have been opened. 13. Do not rapid cycle compressor. Compressor must be off 3 minutes to allow pressures to equalize between high and low s.ide before starting. 14. Wire not present if HPS, LPS or CTD are used.

Figure 17-43 use this diagram to answer Review Question 29.

340

UNIT 17

LVJB

CONTROL BOX

YL-Y]

BL-C

LVJB COLOR CODE BLACK BK BLUE BL BR BROWN OR ORANGE PU PURPLE RD RED \\:'H \VHlTE YL YELLO\V

BK )L BK RD I

BL

L� TI,•T2} 3� on

-YL·

)

\,YIRING CODE FACTORY WIRING HIGH VOLTAGE LO\V VOLTAGE OPTIONAL HIGH VOLTAGE - - - -

.L

-LlOL20L30

RD PU

-�!�, PU•

AlJX IO

\(� / CIVI

BRBK-

YL

FC

I

'/

'J

I

BR

I

1--�1

I

RD

I

1

\

\I

/I

I

I

BK

�

f

FIELD \VlRlNG HIGH VOLTAGE - - - - LOW VOLTAGE - - - - -

EQUIPtvfENT GROUND USE COPPER CONDUCTORS ONLY

@

C01\1P

Figure 17-44 Use this diagram to answer Review Questions 30 and 31.

COlVIPONENT CODE CONTACTOR C OUTDOOR FAN MOTOR C.tv1 COMP_ CO.tv1PRESSOR FC FAN CAPACITOR INTERNAL OVERLOAD 10 LVIB_ LOW VOLTAGE JUNCTION BOX

CONTROLS SHO\\-'N WITH THERtvIOS TAT lN

UNDERSTANDING ELECTRICAL DIAGRAMS

Figure 17-45 use this diagram to answer Review Question 32.

341

UNIT 18

Resistors WHAT YOU SHOULD KNOW After studying this unit, you will be able to: 1. List types of resistors. 2. Describe resistor ratings. 3. use the resistance color code to determine resistance. 4. Calculate the resistance of a color-coded resistor. s. Determine resistor tolerance.

A resistor is used to drop the voltage in an electrical circuit. In HVACR it is used on circuit boards and to discharge start capacitors. Resistors are also found in oil safety sv.1itches as a vvay to reduce incoming voltage. It is valuable to learn so1ne­ thing about these components because they may come into play during your troubleshooting activities. For example, you find a burned-out resistor on a circuit board. The board should be replaced, but what if it is not available or the order time is too long? Replacing the resistor is a repair long shot, but it might v.rork. You should investigate the reason for the burn-out. Maybe vvires touching each other caused the resis­ tor to burn open. It is v.rorth the chance of trying to repair it-but don't get too excited, because in many cases the resis­ tor burned out because of some other defective con1ponent that may not be so obvious. This unit provides the essentials of ho,At to select a resis­ tor for a particular job. It is ahvays best to go ,vith an exact replacen1ent, but ,..,,.hat do all those color bands n1ean? Let's take a look at the ansv.1er to that question.

TECH TIP Two-watt, 470,000-il (470-k.fl) resistors are found across the terminals of start capacitors. The resistor may be soldered or connected using a quick-connect slip-on con­ nector. The purpose of the resistor is to discharge the capacitor immediately after power is removed from this component. Remove the resistor when checking the capacitor. Replace the resistor across the capacitor terminals prior to placing the capacitor in service. The resistor is used to discharge the capacitor, thus preventing the charge from damaging the motor in a short cycling condition.

18.2 TYPES OF RESISTORS The hA/O co1nmon types of resistors are the carbon resistor and wire-wound resistor. Carbon resistors use various grades and quantities of carbon ,-vrapped in a sn1all insulated cylin­ der (see Figure 18-1). A \-Vire-·wound resistor is n1ade of resistive 1netal alloy such as nickel-chrome ,-vire wrapped in an insulated shell (see Figure 18-2). Son1e ,vire-,-vound resistors have a hollo\-v core that helps dissipate heat fro1n the device. Hollffw-core \\rire-\\'Ound resistors should be installed in a vertical posi­ tion so that heat can rise through the chin1ney of the resistor.

18.1 THE RESISTOR A resistor is designed to slovv do\'vn or oppose cur­ rent flow·. As mentioned earlier, resistors are con1monly used in modern HVACR equipment and on circuit boards, across capacitors, and in o.il safety S\-Vitches. Like many components in our profession, the resistor is basi­ cally ignored because it is a reliable component that rarely causes a problem. Electric heat strips and crankcase heaters are also resis­ tors. This unit, ho,vever, focuses on the resistor co1nponent that is used to reduce current flo,v and not heat air or a fluid. 342

Figure 18-1 on these carbon resistors, the color of the band

represents the resistance and the tolerance.

RESISTORS

343

temperature should be near the ambient temperature around the component. Resistors can operate below 0° F and above 200° F v,rith little impact on their performance. Some resistive materials vary with temperature, but they are not covered in this unit. Most resistors have a maximum voltage range of 200 to 600 volts. The temperature or voltage range is usually not a concern since the resistor is designed and tested for the application.

18.5 TOLERANCE Figure 18-2 Wire-wound resistors use nickel-chrome wire, which offers resistance to electron flow.

18.3 POWER RATING




344

UNIT 18 The standard resistor color code table:

orange

Yellow Green

Gray White

1st digit

2nd digit

3rd digit*

Multiplier

0

0

0

x10°

1

1

1

x10 1

±1%

2

2

2

x102

±2%

3

3

3

X103

4

4

4

X104

5

5

5

X105

±0.5%

6

6

6

X106

±0.25%

7 8

7

7

X107

±0.1%

8 9

8 9

X108

±0.05%

9

Gold

Silver None

Tolerance

X109 x0.1

±5%

X0.01

±10% ±20%

* 3rd digit - only for 5-band resistors Figure 18-4 This table explains the color code that will help you identify the value of a resistor based on its color band. The "1st digit"

and "2nd digit" columns are the first two numbers of the resistance. The "3rd digit" column, shaded in gray, is an additional number for use on five-band resistors. The "Multiplier" column is the number used to multiply the first two digits. The "Tolerance" column is the percentage range expected of the resistor. Common tolerance indicators are gold, silver, and no band at all.

band is the tolerance of the resistor. The normal tolerance is +5%, +10%, or +20%. Som.e precision resistors have a fifth color band of brow · n. The bro\.vn band, as sho,vn at right in Figure 18-5, represents a +1% tolerance rating. There is no standard for the fifth band. The bro,vn band on the upper part of a resistor indicates that it is a precision resistor.

A five-band resistor uses a different formula to calculate resistance. The five-band resistor uses the first three bands as numbers. The fourth band is the 1nultiplier, and the fifth band is the tolerance band. Using Figure 18-4 and the sample resistor sho,vn in Fi.gure 18-5, ,-ve can detennine that a resi.s­ tor with bro,o\'11., black, black, red, and bro,vn color bands ·will be 1,000 n. (1 kfl) (because the red 1nultiplier band adds t\-vo zeros). So Figure 18-5 sho,vs a 1,000-0 resistor ,-vith a +1% tolerance. The tolerance \.Vill vary from one manufacturing con1pany to another; the fifth band may indicate 2%, 1 %, 0.5%, or an even closer tolerance, according to each manu­ facturer's o,vn standards. Let's work a couple of exan,ples to determine resistance.

EXAMPLE 18.1 CALCULATING RESISTANCE: RESISTOR WITH FOUR BANDS

l l

Figure 18-5 These are carbon resistors. The color band count

starts on the left side with brown, blacl-- -

----------- --------------------, HEATER ELEMENT

PURPLE

I

LI

FAN l\10T0R

BLACK

S\V. SIDE

I I I

-b- --6

FUSED THERMO LINK CUTOUT

L2

'-------------------------------�

S\.VITCH BACK

COMPRESSOR RUN \VIRE TO BE HOOKED TO RED DOT STDE OF CAPACITOR.

TAN ORANGE

RED DOT

YELLOW

..... ::r: ::::: �

I

OVERLOAD

-< 3 T I I

2

THERl\lI0STAT

YELLOW

0 BLACK

COMPRESSOR

Figure 21-17 use this diagram to answer Review Questions 1, 2, and 3.

RUN CAPACITOR

389

390

UNIT 21 SCHEMATIC DIAGRAM (LADDER FORM) I I I I

-EQUIP

Ll I

I

COi\1P

CONT

I

.L

GND

L2 I I I I I I I I I

5

*CHS

*ST

2 *SR

*CH

F "'--t::2..JCAP

(NOTE#I4) *LPS

*DTS

CONT

*HPS

T2 Tl

*LLS

©----

*CTD

T3

I I

�R

:

©------------------------------------1�--------------------------� R

C

I I

:

®-------------------------------------�--------------------------J

INDOOR THERMOSTAT

EXTERNAL POWER SUPPLY 24 V

Figure 21-18 Use this diagram to answer Review Questions 5, 6, and 7.

UNIT 22

Gas Heating Systems WHAT YOU NEED TO KNOW After studying this unit, you will be able to: 1. Explain how gas heating systems are categorized by efficiency. 2. Describe a gas-burning cycle. 3. Identify basic gas-burning controls. 4. Describe the operation of three components found on a low-efficiency gas furnace. s. Using an electrical diagram, identify which components of a gas furnace use line voltage and which ones use control voltage. 6. Identify safety controls in a gas furnace wiring diagram. 7. Describe two types of troubleshooting techniques used when working on gas furnaces.

Gas heating systems can be very siinple or very co1nplex.

The si1nplest gas-burning systems are those that have the fe,.vest electrical controls. Some gas heating systems have only a gas valve and a temperature control to turn the gas valve on vvhen the temperature drops in a room and turn it off "vhen the set temperature is reached. These systems are typically gas space heaters that do not have a blo,ver to move air through the unit and into the room. In this unit, a simple gas heating systen, \vith a blov.'er is discussed. For contrast, ,.ve also present a complex and highly efficient heating system. The differences bet\veen these nvo systen1s will illustrate the differences in operation required to efficiently control and 1nonitor a gas-burning systen1. More co1nplex systen1s require additional electrical control and monitoring devices. As the complexity increases, the techni­ cian is required to kno"v and understand more about electri­ cal and electronic controls. Also, as a system's co1nplexity increases, manufactur­ ers provide additional tools that the technician can use to troubleshoot systems. Circuit boards provide basic trouble­ shooting codes that can be interpreted by the technician. Troubleshooting codes usually take the fonn of flashing lights on the circuit board. The number of flashes is an indi­ cation of the problem. For exarnple, t"vo flashes repeated every 10 seconds may 1nean that the voltage polarity is incor­ rect. Some equipn1ent is so sophisticated that it ,vill register a problem on the thermostat or at a connected laptop at the custon1er' s location. Troubleshooting flo\vcharts are provided to help guide the technician in conducting the troubleshooting procedure.

While both of these things are helpful, the technician must rely on practicing the troubleshooting sequence in a certain ay. Just like "hopscotch," the troubleshooting process relies on the technician taking the correct readings in a sequential way to determine if a co1nponent is receiving the right volt­ age or if a s\vitch is open rather than closed. By the end of this unit, you ,vill have a better idea of: 1

\\

■ The similarities and differences bet,veen gas heating systems ■ The operation fro1n start-up, through the heating process, to shutdo,-vn ■ Troubleshooting techniques, processes, and tools available for systen1s at each end of the efficiency spectrum.

22.1 CLASSIFYING GAS HEATING SYSTEM TYPES Gas heating systems can be classified in several 'Nays. Natural and LP (liquefied petroleum, also knO\V11 as propane or bu­ tane) are the t,vo commercial gases that are distributed for general consun1ption. Units are typically designated and sold as either one or the other type of gas-burning wut. More often, ho\'\rever, gas-burning units are set up as natural gas units, and if a unit needs to be used with LP, an "LP kit" is purchased or provided by the manufacturer to convert the unit from natural gas to LP.

SAFETY TIP Liquefied petroleum gas is heavier than air, so it can pool in low areas or be confined in a small room. Natural gas is lighter than air and rises. Small gas leaks can result in large explosions that can kill. Before operating any electrical component (gas furnace, electric light switch, etc.), smell for the presence of gas. In their natural state these gases are odorless, so a strong odorant is added to give them a distinct smell. some gas companies have stated that it smells like rotten eggs. If you can smell gas, ventilate the area before you begin working. If you smell gas before entering the furnace area, it would be advisable to call the fire department or gas company for assistance and do not turn on the light or any other spark-creating device. 391

392

UNIT 22

22.2 VENTING SYSTEMS AND EFFICIENCY Gas heating system.s are also classified by their efficiency, w·hich relates to how· they are vented. Venting is the process of removing the combustion by-products of burned gas fuel. The relationship of efficiency to venting has to do ,"lith the temperature of the exhaust or chimney gas. Lo,-v-efficiency units do not extract enough heat from the burning gas to reduce exhaust vent gas temperatures. Temperatures of up to 300°F can be measured at the chimney connection for lo,v­ efficiency units that are rated fron1 60% to 78% efficient. lvlid-efficiency units (between 80% and 85% efficient) ex­ tract more heat and reduce the exhaust gas temperature to around 210° to 250° F. The venting required for lo,-v- and mid-efficiency gas furnaces is classified as a Type B venting syste1n and typi­ cally consists of a double-,valled vent pipe. In son1e cases, a stainless pipe that can resist corrosion fro1n acid is used. Acid is created in the exhaust or flue gas, because when the venting temperature drops belO'w 212°F, 1noisture that con­ tains acid can condense out of the flue gas and collect in the vent pipe. When flue gas te1nperatures drop to as lo\v as 120° F, the exhaust temperature is lo,.v enough to allow the use of plastic pipe as a vent material instead of metal pipe. Plastic resists corrosion fron1 acid and can be easily sealed so that both condensing moisture and exhaust gases are completely isolated from the living space. By extracting the n1aximum amount of heat and exhausting flue gas at the low·est possible temperature, gas furnace efficiencies of n1ore than 90% can be achieved. Son1e modern fur­ naces have even been rated 98% efficient. Units \\rith this type of efficiency are classified as high-efficiency gas heat­ ing systen1s. Both natural gas and LP heating syste1ns can qualify for these high-efficiency classifications. The more efficient the gas furnace, the higher its cost, as shown in Table 22-1.

Table 22-1 Furnace Efficiency vs. Cost Efficiency Type

Efficiency Rating

Furnace cost

vent Type

(AFUE)

Highefficiency

Plastic vent

90% and higher

High

Midefficiency

Double wall (or possibly stainless vent)

80°/2 to 85%

Midrange

LOW-

Double wall vent

Below 80%

LOW

efficiency

U.S. Government

Federal law prohibits removal of this label before consumer purchase

XYZ Corporation ModelABC-L

Furnace - Natural Gas DIRECTVEN1 UPFLOW

78.0 Least Efficient DIRECTVENT DOWNFLOW

78,0 Least Efficient DIRECTVENT HORIZONTAL

78,0 least Efficient

Annual Fuel Utilization Efficiency

9S.O

Y

96.6 Efficiency Range of Similar Models Most Efficient

'

Annual Fuel Utilization Efficiency

92.3

I

96.6 Efficiency Range of Similar Models Most Efficient Annual Fuel Utilization Efficiency

94.7 , 96.6 Efficiency Range of Similar Models Most Efficient

• Efficiency range based only on natural gas furnaces. • For more information, visit www.ftc.gov/appliances.

Figure 22-1 An EnergyGuide label, as mandated by the Department of Energy.

u.s.

GREEN TIP Most modern gas furnaces have an AFUE (annual fuel utilization efficiency) rating. Figure 22-1 shows the AFUE label that you will find on a new gas furnace. AFUE is the amount of heat that goes into conditioned space versus the amount of heat developed by burning the gas fuel. A furnace manufacturer completes a complex set of test­ ing standards to determine a furnace's AFUE rating. A simple, but not totally correct way of viewing AFUE is expressed in the following formula: AFUE

=

Btuh output Btuh input

The U.S. Department of Energy (DOE) has mandated that furnaces have a minimum AFUE rating of 80%. warmer climates tend to use lower AFUE systems, while colder climates use higher AFUE systems. The DOE man­ dates use of the EnergyGuide label, as shown in Figure 22-1, which estimates the actual energy consumption of an appliance and provides some information about whether that consumption is above or below the aver­ age for that type of product. The dollar amount at the bottom of the EnergyGuide label is the estimated yearly

GAS HEATING SYSTEMS

393

GREEN TIP

ENERGY STAR Figure 22-2 The ENERGY STAR label is the government's

symbol for energy efficiency.

operating cost based on the national average cost of electricity or other fuel usage. The ENERGY STAR label shown in Figure 22-2 is the government's symbol for energy efficiency. It helps con­ sumers easily recognize highly efficient products, homes, and buildings that save consumers energy and money and help protect the environment. The ENERGY STAR label often appears at the bottom of the EnergyGuide label for qualified products. The most efficient gas furnaces may have the ENERGY STAR label. They will have an AFUE of 85% and higher and have a high-efficiency blower (ECM).

TECH TIP The National Fuel Gas Code and other national standards (ANSI Z223.1, Z21.47, 221.10.3, and Z21.13) categorize gas appliances according to their type of venting, as listed in Table 22-2. In addition to fuel, efficiency, and venting classifications, gas heating units can be further classified by such things as: ■ ■ ■ ■

Type of ignition system Type of gas control Type of fan/blower control The direction in which air is moved through the unit (upflow, counter flow, and horizontal).

Each type of system will use different electrical and electronic control devices, which makes each type of gas heating system distinct in terms of its electrical components and configurations. Table 22-2 Gas Appliance Categories category

II

venting

condensing

venting Material

Gravity

No

B vent

Gravity

Yes

Per manufacturer

Ill

Fanassisted

No

Stainless

IV

Powered

Yes

Plastic

More on Green Heating Systems Gas heating systems can be classified as "green systems." The term green has many definitions, but if a unit is referred to as green, then it is being compared to another unit that uses energy less efficiently. The AFUE efficiency rating of a gas-burning appliance is listed by the manufacturer and is displayed as an EnergyGuide yellow sticker on new sys­ tems. As mentioned earlier, the AFUE rating refers to the percentage of fuel that is extracted as usable heat to warm a space. The higher the AFUE number, the less energy a system wastes and the more it is considered to be "green." Standard heating systems with standing pilots (pilots that burn continuously) are considered less green than fan-assisted 78% (78 AFUE) systems. The 90 AFUE sys­ tems are greener than the 80 AFUE models. The closer a system is to a 100% AFUE rating, the more green the system is, because a high AFUE rating means that most of the heat goes into the space being heated, rather than being vented to the outside. Some gas furnaces have AFUE ratings as high as 98%, meaning that a very minimal amount of heat is vented outside. As gas heating systems become greener, they be­ come electrically complicated. There are more compo­ nents to help it become more efficient and more controls to monitor the operation. Very simply, a gas-burning appli­ ance can be monitored by a human being: Gas is turned on, the flame is lit, and the flame is extinguished at the end of use. When basic controls are applied, the gas heat­ ing system can be turned on and off automatically with a thermostat. While the system is burning gas, the operation can be monitored and turned off if a safety issue occurs. In a later section on furnace operation, a simple gas heating system will be described as it moves from one sequence to the next. The basic operation of a gas­ burning appliance will be described. This is the same sequence of operation that more sophisticated furnaces follow with the exception that more sophisticated fur­ naces require additional steps. The additional steps have to do with the extra electrical components that are used to increase efficiency to become "greener."

TECH TIP Power-nothing works unless line voltage is received. Always ensure that the line voltage and control voltage are present by using the voltmeter. When the blower door is removed, the door switch will turn off power to the unit. This is a safety switch. If at all possible, service electrical systems with the power off.

SAFETY TIP If the system needs to be powered with the door off, manually close the switch rather than use a jumper. Be sure to check that this switch operates before conclud­ ing a service call. While checking with the power on, be sure to use good electrical safety procedures.

394

UNIT 22

22.3 GAS FURNACE COMPONENTS This section explores the common electrical co1nponents found in a forced-air gas furnace. After this explanation ,,ve '"'ill explore how these co1nponents work together as a gas furnace. Here is a list of comn1on electrical iten1s that you may find on a gas furnace: ■

■ ■ ■ ■

■

■

■

■

Door switch Gasvalve Inducer fan assembly (air proving switch) Hot surface igniter Flame detector (flame rod) High limit switch Flrune rollout switch Circuit board Blower motor assembly.

vVe v\rill be using esti1nates on the timing sequence of oper­ ation. For example, one manufacturer may activate the system blower automatically after 60 seconds, vvhile another may de­ sign it to come on 90 seconds after the beginning of the heating cycle. Some circuit boards have options to start the blo,ver at different ti1ne intervals. Others are preset to energize at a pre­ scribed time. v\Then a time, resistance, or something specific is mentioned, ren1ember that it ·will vary among manufacturers.

22.4 DOOR SWITCHES The door s,vitch sho,vn in Figure 22-3 is used to prevent a furnace from operating without the blo,,rer door panel. The door s,vitch is a rocker s·witch that opens if the panel

Figure 22-3 The door switch is

a rocker switch that opens if the panel is removed.

is removed. This door s,vitch has been bypassed and forced closed ,-vith a nylon tie while it is being serviced. The nylon tie or other byp ass 1neasure must be removed to engage the safety feature of the door switch. If the furnace ,vere allow·ed to operate ,vithout the blo,ver door cover, the burned gases could be pulled into the return air stream and distributed to the conditioned space. This could be dangerous if these vent gases included carbon 1nonoxide. Carbon monoxide is not always present in burned fuel, but ,vhy take a chance? Ahvays remove the bypass before reinstalling the blo,ver door.

SAFETY TIP A carbon monoxide (CO) detector should be installed in every building that has a fuel-burning appliance within its structure. The best carbon monoxide detector will be battery operated and installed on or near the ceiling. A power failure will not affect the operation of a battery­ operated detector. co is lighter than air, therefore the detector should be installed high on a wall or on the ceiling. Even a building without fuel-burning appliances can have high co levels. For example, parking a run­ ning car in a garage or below a building will create a poison danger to people in the building. co is odorless, tasteless, and cannot be seen in the air. Have everyone vacate the area if the co detector sounds. Call the fire department.

GAS HEATING SYSTEMS Table 22-3 carbon Monoxide Poisoning Levels (in parts per million)

f\.1AIN SOLENOID �

carbon Monoxide: (CO} Product of Incomplete Combustion

395

PILOT SOLENOID '

RE:MOVECAP TO ADJUST GAS PRESSURE

100 PPM - Safe for continuous exposure 200 PPM - Slight effect after six (6) hours 400 PPM - Headache after three (3) hours 900 PPM - Headache and nausea after one (1) hour 1,000 PPM - Death on long exposure 1,500 PPM - Death after one (1) hour Most codes specify that co concentrations shall not exceed 50 PPM

Figure 22-4 This is an older style gas valve with a pilot light

solenoid and a main solenoid valve. The light blue knob is the ON/OFF selector. It is in the ON position.

SAFETY TIP Table 22-3 shows various carbon monoxide exposure levels and their consequences. When natural gas (CH4) with the help of two oxygen molecules (02) burns, it cre­ ates heat, carbon dioxide (CO2), and water (H20). Stated as a formula: CH 4 + 2 0 2

=

CO2 + 2 H 2 0

This is perfect combustion. Carbon monoxide is formed if there is not enough air for the combustion process or if the flame is not at a high enough tempera­ ture, which can occur if the flame is touching the heat exchanger or burner tubes. Anything that interferes with complete combustion may cause co to form.

22.5 GAS VALVES Gas valves, like those sho-..vn in Figures 22-4 and 22-5, are control valves used to 1neter the flow of gas to the burners. A natural gas valve also reduces the pressure from the gas supply, \vhereas a propane gas valve does little to control the pressure of the gas supply. The gas valve is a solenoid valve, therefore it has a coil that is energized to open by 24 volts in 1nost cases. The sole­ noid coil may be a low- or high-resistance coil. The resistance of so1ne coils is as lov, as l 00 fl, ,vhereas others 1nay have as much as a n1illion ohms of resistance. Use a DMM '"''ith a high resistance (more than 1 Mil) to determine if the gas valve coil is good. If the control voltage is measured at the gas

Figure 22-5 common gas valve on a gas

furnace. The gas line will be installed on the left side of the valve when the yellow protective cap is removed. The gas line going through the furnace wall should be hard pipe. The valve is in the OFF position.

396

UNIT 22

Figure 22-6 The gas connection should be hard

pipe to the point where it penetrates the furnace cabinet.

valve, it should click open. If the control voltage is present on the valve and it does not open, it needs to be replaced. The gas piping should be a piece of hard pipe from the gas valve until the point where it penetrates the furnace ,vall, as sho,vn in Figure 22-6. A flexible connector going through the furnace ,vall may develop a leak if it rubs the penetration point. Many local codes require a hard pipe in­ stallation inside the furnace housing. A flexible connector has a thin wall compared to hard pipe. The use of flexible tubing penetrating the cabinet could possibly lead to a gas leak if the furnace vibrations cut into the thin flexible con­ nector surface. Yellow or blue, gas-approved Teflon tape is used to seal the joints.

22.6 INDUCER FAN ASSEMBLY An inducer fan motor is a simple shaded pole motor ( see Figure 22-7). Some of these motors are three-phase ECl\1 1notors, ,-vhich therefore must be checked as three-phase 1no­ tors. This is the first device to be energized in the heating cy­ cle. You can hear it operate at the beginning of the cycle. The inducer fan motor vvill con1e on to purge the heat exchanger prior to firing the burners. It ,vill operate for about 15 to 20 seconds before the igniter is energized. Modern heat exchanger designs are more efficient than older designs, but also more restrictive to the air­ flow through it. That is why an inducer fan is needed that can pull the flue gas from the heat exchanger and push it into the venting system. It is important for the vent pipe to have good flo"v for the flue gases. The inducer fan as­ sen1bly has an air proving svvitch that closes when there is adequate venting po,ver through the heat exchanger and into the vent. \,Vhen the s,vitch closes it allo,,vs the heating sequence to continue to the next step. In Figure 22-7, no­ tice the gray hose attached to the air proving s,vitch on the inducer housing.

As sho'\-vn in Figure 22-8, the airflo,.v can be checked by placing a tee in the hose and measuring the very low, negative air pressure. In this case, a negative pressure w·ill be measured since the 1nanometer fluid is being pulled toward the hose connection. A manon1eter or lvlagnehelic® is tied into the hose to measure pressure in inches of ·water column, ·which is abbre­ viated WC. The ,-vater n1anometer or a pressure differential gauge can also be used to measure this lo\v air pressure. For exainple, a reading of 0.42"WC or greater might be accept­ able. If the airflo,,v is restricted, the inducer ·will develop less than the required pressure to close the air proving s,vitch. A reading near 0.00"\VC ,vould 1nean no vacuum or negative air pressure. This condition is n1ost likely the result of an air restriction in the venting system or the motor may not be turning at the correct RPMs to vent properly.

22.7 HOT SURFACE IGNITERS Generally, after the inducer fan purges the heat exchanger and there is positive airflov.,, a hot surface igniter (HSI) is activated. The HSI is a hot glowing element used to ignite the gas. The HSI replaces the older style, continuously burning pilot light, which improves energy efficiency. It operates on 120 volts. There are t\.vo types ofHSis: ■ Silicon carbide ■ Silicon nitride. The silicon carbide igniter is used on older gas furnaces. It has a resistance of about 11 to 20 !l. The carbide is very delicate and breaks easily. It is designed in the shape of a squeezed M. When replacing this type of burned-out HSI, do not touch the replacen1ent igniter. Dirt or oil from your fingers will affect performance. This type of HSI may have a hairline crack that is visually undetectable but ,-vill not get hot

Figure 22-7 An inducer fan motor assembly is used to purge the heat exchanger and develop exhausting of the flue gases.

HOSETO---:::i� MON'ITOR AIRFLO\V

INDUCED DRAF MOTOR ASSEM ...........

NEGATIVE PRESSURE PULLS THE FLUID UP

____,..-....._

0-2 IN. SLOl'E GAUGt;

L'ICL.JNE MANOMETER

_______. TWO AIR PROVING S\VlTCHES TEE CONNECTION ADDED

Figure 22-8 This furnace is a two-stage gas furnace. It has two air proving switches and two stages of forced venting. one switch is for first or low stage heat, and the other is for high or second stage heat. Low heat has less power venting. In this example, an incline manometer is used to test the negative pressure developed by the operation of the inducer fan assembly. 397

398

UNIT 22

Figure 22-9 In this silicone carbide installation,

you are looking at the back side of the igniter as found in the controls area. The other end of the igniter is in the burner gas stream. Note that 120 volts is needed to heat up the silicone carbide and cause the gas to ignite.

board ,vill close the gas valve. The heating cycle may start again after a delay. Son1e designs \.vill retry ignition a fe,v tin1es, then lock out. Lockout is the term used for not al­ lov:ing the gas to cycle additional tin1es until the po,ver has been interrupted. The lockout is a safety device that can shut do\'\111 the system to prevent ra,v gas from building up in the furnace. A fla1ne detector or flame rod is used to determine if a flame is present after the gas burner ignites. A flan1e detec­ tor is installed in the burner fla1ne path and connected to ground. The other end is usually connected to the circuit board, and if a sn1all n1icroamp current flo,-v to ground is not established in seconds, the control board ,,,ill shut down the heating cycle. If a flame is present across the sen­ sor, a low-current DC signal ,,rill be developed in the rod and the circuit board ,vill allo\'\ the heating operation to continue. Figure 22-11 shows the end of the sensor that connects to the circuit board. The other end of the flame sensor (not seen) will sense the burner flame and allo·w the heating cycle to continue. Figure 22-12 is a flan1e sensor with a part of the porcelain missing. This may affect the performance of the sensor. The flame sensor adjustment is critical and ¼rill vary among designs. Figure 22-13 illustrates one manufacturer's installation reco1nmendations to ensure that the sensor ,viJl do its job. Figure 22-14 shows ho"Vv to check the function of the flame sensor. When the sensor "feels" the flame heat, a low current ,vill be generated bet\•veen the flame sensor and the circuit board. Depending on the manufacturer and design, a current flo,-v signal measured in microamps (as lo,-v as 3 to 8 µA DC) n1ay be adequate to allo"'' the heating cycle to con­ tinue. The DC nucroamp meter must be placed in series with the flame sensor ,vhen taking this reading. The placement of the sensor in the flame is important to develop the proper lo,-v-current signal. The sensor cannot be grounded or the 7

Figure 22-10 This is a silicon nitride hot surface igniter. It is tough

and longer lasting compared to a silicon carbine HSI. It is energized for a short period of time to ignite the gas by a 120-v circuit.

enough to ignite the gas. The back side of a carbide igniter is sho\.vn in Figure 22-9. The carbide igniter is placed in the gas bun1er field. Figure 22-10 sho\'\'S a silicon nitride igniter. It is an up­ grade in technology in that this igniter is very tough. It looks son1ewhat like a flat nail. The resistance of a good silicon ni­ tride i.gniter is in the range of 40 to 75 n. For both of these HSis, high resistance is an indication that its life is about over. Higher resistance ,vill also reduce its heat output, impairing its ability to light off the gas.

22.8 FLAME SENSORS Modern furnaces use a fla1ne detector or fla1ne sensor to determine if a flan1e is present. It is also called a flame rod. If a flame is not detected in a fe,v seconds or less, the circuit

GAS HEATING SYSTEMS

399

Figure 22-11 This is the back side of the flame sensor. The purpose of the flame sensor is to verify that a flame is indeed present, allowing the gas valve to continue to release gas.

lo,v current ,vill not reach the circuit board. This ,vould stop the heating operation. The flame sensor should not be cleaned with sandpaper. Use steel ,-vool or a scrubbing pad to remove buildup on the rod. Figure 22-15 sho,vs another type of flame sensor used in older style furnaces that have a continuously burning pilot light. This is a thermocouple used to sense the pilot light. The other end of the thern1ocouple is screv.1ed into the gas valve. When the pilot burns across the upper half of the thermocouple, it generates a 20- to 30-millivolt DC signal that v.1ill energize a solenoid in the gas valve, allo\\1ing gas to flo,v on den1and. The gas valve ,vill open \\1hen there is a call for heat. Figure 22-16 shov.1s hovv to measure DC millivolt out­ put. It will take the thern1ocouple a minute or two to develop full voltage w-hen exposed to the initial pilot fla1ne.

FLAf.1E SENSOR --

BROKEN PORCELAIN

Figure 22-12 This is a flame sensor, also call a flame detector or flame rod. Notice how the porcelain insulator is broken. This might create a problem for flame sensing if it touches the furnace chassis or ground.

�--0.71

0

0.57

0

0

0

(l)

1.645

0

HOT SURFACE IGNITER

FLAI.\IIB SENSOR

0

Figure 22-13 This is a manufacturer's recommendation for the installation of a hot surface igniter and the placement of the flame sensor.

400

UNIT 22

Figure 22-14 This is the setup to check the microamp current flow through a flame sensor. The DC voltmeter is placed in series with the flame sensor and circuit board. Depending on the design conditions, a range of 3 to 8 microamps (µa) DC may be adequate to allow heating to continue.

FLANlE SENSOR

DIGITAL VOLTMETER

I

FLA�ffi SENSOR \VIRE

,---OBSERVE

POLARITY

t 8MV OR HlGHER

MILLIVOLT METER

THEAAIOCOUPLE SENSOR

Figure 22-15 This thermocouple is used to sense the pilot light on the older style standing pilot furnaces. The other end of the thermocouple is screwed into the gas valve.

22. 9 HIGH LIMIT SWITCHES The high limit switch, as shown in Figure 22-17, is like an eyeball that "sees" excessive heat in the furnace heat ex­ changer section. Figure 22-18 shows a closer vie,v of the same limit S'\-vitch. It is a bimetal s,vitch that opens when the ternperature around it rises above a set temperature. Some high limits are set to open at 180°F; others are set to higher temperatures. Most of these devices are auton1atically reset after they open, meaning that w·hen they cool they v.,ill snap closed again, allo'\-ving the heating cycle to start again.

Figure 22-16 This shows how to measure the DC millivolt output of a thermocouple.

If the high limit sv.1itch is defective, it will have to be replaced w·ith the exact same part. Substituting a limit sv.1itch at a clifferent rating ,vill leave you open to a serious la\.vsuit if a fw·nace fire occurs-even if the fire is not related to the high limit s,vitch. Figtu-e 22-19 sho\-vs the sa1ne limit s,vitch again, but this is the back side of it, which is in the control section of the gas furnace. You can remove the wire fron1 one side of the limit s,-vitch and check for continuity. Resistance should be near 0 n.. Removing the louvered furnace panel ,vill reveal the high limit switch and other critical controls.

GAS HEATING SYSTEMS Figure 22-17 This is a view of a gas furnace

401

-

before it is installed. This furnace has a tubular heat exchanger. The high limit switch is seen on the right. This area will get excessively hot if there is a lack of airflow.

Tripping or opening of the high limit S\.Vitch is usually caused by low· or no airflovv. For example, the air filter or evaporator 1nay be dirty. The blower motor may be off or the blo,-ver squirrel cage dirty. Anything that reduces the airflo,v significantly ,vill cause the high lin1it s,vitch to open. Finally, Figure 22-20 shows an extended high limit svvitch found in the air stream of some gas furnaces. The extended device "sees" or "senses" the airflo,v better since it extends into the air stream. Most of these high limit devices are of the automatic reset design. Most high limit s,vitches fail because they were toggling on high temperatures.

I

22.10 FLAME ROLLOUT SWITCHES The flame rollout s,vitch is really a high limit switch that must be reset manually. Figure 22-21 sho,vs the red reset button on a flame rollout s,vitch. A flame rollout is a very danger­ ous event because it means the flames have reached into the

Figure 22-18 This is the same furnace shown in Figure 22-17,

but in a closer view. Notice how the high limit switch resembles an eyeball.

402

UNIT 22

•

Figure 22-19 This shows the back side of the

high limit switch from Figure 22-17 in the control section of the gas furnace. Removing the louvered furnace panel will reveal the high limit switch and other critical controls.

HIGH LilYUT SWITC IN THE GONTROJ..;S AA.EA

WIRE CONNECTION TERl\1INALS

i

-- SENSOR HEAD

Figure 22-20 Depending on the design this high limit switch

extends 3 to 4 inches into the furnace airflow stream. The bimetal sensor head is about the size of a dime.

furnace control area from the burner area. This can burn ,vires or start a furnace fire. For this reason, a roll.out s,�ri.tch must ahvays be of the manual reset design. You will need to push a reset button to close the svritch. A tech needs to check out this condition. Fla1ne rollout 1nay be caused by inadequate vent­ ing, a lack of combustion air, or very high gas pressures. To test this safety switch, remove voltage and a ,-vire fro1n one side to test for continuity. Push the red button. Expect O fl if the switch is good. As ·with any safety device, replace the s,-vitch ,-vith a like device.

TECH TIP A high number of the circuit boards returned to distribu­ tors do not have any problems. one distributor reports over 50% returns that have no problem. Use routine checks before condemning a board: Check for a good equipment ground, 120-v polarity, connections, manu­ facturer's troubleshooting sequence, etc.

GAS HEATING SYSTEMS

403

Figure 22-21 Flame rollout switches are installed near the burners in case flames back up out of the burner compartments. Flame rollout switches are manual reset safety devices. Remove voltage and a wire from one side to test for continuity.

22.11 CIRCUIT BOARDS The circuit or control board, as show·n in Figure 22-22, is the brain of a furnace system. It controls signals to the gas valve and blov1er operation. It keeps the furnace operation safe if one of the external safety devices opens or sends a problem signal. Many circuit boards provide a technician ,vith LED flashing fault codes, airflo,v status, and CFlvls. Table 22-4 is a sa1nple fault code table si1nilar to those

found on the inside of the panel door of the blower section of a gas furnace. A circuit board contains high- and low-voltage con­ nections. It also has a control voltage fuse in the range of 3 to 5 an1ps. Always use the same size or a smaller replacement fuse. The board can usually handle up to 10 amps for blo,ver motor operation. A transformer may be mounted on the board or simply attached as sho"vn in the low·er right side of Figure 22-22.

Figure 22-22 This is a circuit board used in a residential gas furnace. This control board is the brain of the system.

404

UNIT 22

Table 22-4 Sample Fault Code Table Error Code

LED Indication

Normal Operation

on

Hardware Failure

Off

Fan On/Off Modified

1 Flash

Limit Switch Fault

2 Flashes

Flame Sensing Fault

3 Flashes

4 consecutive Limit switch Trips

4 Flashes

Ignition Lockout Fault

5 Flashes

Induced Draft Motor Fault

6 Flashes

Rollout switch Fault

7 Flashes

Internal Control Fault

8 Flashes

TECH TIP A dusty or dirty circuit board is an indication of a dirty air filter or leaks in the return air ducts. Check out these problems. use a spray duster, like that used on computers, to gently clean the board. Have your vacuum turned on to remove loose dirt as it breaks loose.

22.12 BLOWER MOTOR ASSEMBLY The blo,-ver motor asse1nbly is behind the circuit board (refer to Figure 22-22). This assembly includes the motor, possi­ bly a run capacitor, the squirrel cage blo·wer, and the blo1,ver housing. Nevv blowers are controlled by a circuit board time­ delay option. vVith this option, a blo,ver can be turned on 60, 90, or 120 seconds after the furnace has been energized. This gives the furnace heat exchanger a chance to ,,varm up prior to blo,ver start-up. The blo,ver may con1e on ,vith a call for heat even if the burner did not fire off for some reason. The blovver cycle is set by the manufacturer and in some cases the tech is given the option of selecting a 60- or 90-second tin1e off delay after the thermostat is satisfied. This gives the blo,ver a chance to purge the residual heat out of the heat exchanger and ductwork. If the blo1,-ver is a PSC motor, it ,vill most likely run on medium speed in the heating mode. If it is an ECJ\1 motor, it vvill ramp up and do,-vn around the call for heat. The ECM will provide smooth starting and stopping and more even airflo,v for the conditioned space.

22.13 LOW-EFFICIENCY GAS FURNACE OPERATION Every gas furnace must be able to do the follo"ving generic sequence of operation in the follov.ring order:

I. The thern1ostat closes because the room temperature has dropped or the temperature has been adjusted to a higher temperature. 2. The control voltage is sent through the thermostat VI/ terminal to start the furnace operating. 3. The inducer draft motor is energized and the air proving switch doses, allo1,ving the next stage to start. 4. The hot surface ignition or standing pilot is ready for the gas supply to begin. 5. The gas valve is energized. It opens, allo1,ving gas to start the ignition process. 6. The flame sensor creates a current flow from the burner flan1e. TI1is establishes that the burners are functioning. 7. The burners ru1d gas rate are adjusted to regulate the supply of fuel and air mixture. 8. The furnace monitors combustion through safety controls. 9. When the heat exchanger ,-varn1s, the blo,ver motor moves heat to the living space though a duct system. 10. The thermostat opens the W circuit because the air has ,,varmed to its setpoint. 11. The gas valve closes and the burners e:xtinguish. 12. The blower shuts dovvn after the heat exchanger cools to around 100°F. This takes about 1 or 2 n1inutes after the burners shut dov.rn. Ho,-v each gas heating syste1n perfonns these operations depends on the design of the unit. The signal received from the thern1ostat in step l of the sequence of operation is typically 24-V po,ver sent through a small set of contacts in the thern1ostat. Contacts close in response to a drop in te1nperature. \:Vhen the contacts close and if the circuit is functional, the control circuit to the gas heating systen1 is complete; the signal is received and the gas unit starts the ignition process.

TECH TIP When a thermostatic switch closes a set of contacts as the result of a drop in temperature, the action is referred to as "close on temperature drop." In this case we are talking about a heating thermostat. Sometimes, the ex­ pression most often heard is "close on drop" and refers to the way the switch works. This can be confusing when describing the operation of a switch that works in the opposite way. If the switch opens on temperature drop (cooling t'stat), instead of closing as described above, it could be identified as an "open on drop" or "close on rise" switch.

The ignition process mentioned in step 5 of the sequence of operations can be very different ,vith each type of gas heat­ ing system. 101,-v-efficiency units have a "standing pilot." A standing pilot is a small flame that is allowed to burn 100% of the time. The standing pilot (see Figure 22-23) is used to

GAS HEATING SYSTEMS STANDING PILOT FLAME �

t

/

INTERNAL WELD

PILOT --SOLENOID VALVE -GAS FLOW

Figure 22-23 The thermocouple develops 20 to 30 millivolts

DC to energize the pilot solenoid valve and open gas flow to the standing pilot flame. This allows the main gas valve (not shown) to send gas to the burners and be ignited by the pilot flame.

405

ignite the main burner when a signal is received from the thermostat. In the case of a standing pilot, the flame is sensed (step 5) through a thermocouple circuit. The thermocouple is a device that is 1nade of t,.vo different metals that are internally "velded at the tip of the thermocouple. When heated, the t\.vo different 111etals cause a \veak electrical voltage of 20 to 30 111V DC to produce a current of electricity. The cur­ rent flo,.v is connected to a coil or solenoid that is ½'Tapped around a movable plunger. \,Vhen the thermocouple is heated, the low current flovv is enough to hold the plunger in the open position and gas flo\vs to the pilot. The current is not strong enough to lift the plunger. The pilot flame is lit while manually holding the plunger up, until the thermo­ couple is heated, ,vhich could take 30 to 90 seconds. If the flame is lost, the plunger drops and stops the flo"v of gas to the pilot. This acts as one of the safety devices (step 4) that n1onitors the flame. Figure 22-24 is a si1nplified diagram for a gas furnace that uses a standing pilot light. The yello,v highlighting in

SAFETY S WITCH &FUSE

FAN CONTROL

BLO\.VER MOTOR

TAP --- lZO V L ,__ __ -.HIGH -. _ _ _ SPEED _ O TS S_E-LE_C_T_E_D L W I L BE FORCOOLTNG

-------------+-t

S TEP DOWN TRANSFORMER

•-------- 24 V OLTS------� T'STAT

GAS VALVE

HIGH LlMTT

THERMOCOUPLE i-+-----

25 MV

----""1

PILOT SOLENOID

Figure 22-24 This is a simplified diagram of a gas furnace with a standing pilot light. Figure 22-25

traces the circuit's operation.

406

UNIT 22

Figure 22-25 The yellow highlighting indicates what is operational prior to a call for heat.

I

SAFETY SWITCH &FUSE

FAN

CONTROL

BLOWER !v1OTOR

IH-----------120VOLTS-----------

STEP DOWN TRANSFORMER

T'STAT

HIGH LTh1IT

GAS VALVE

THERNrOCOUPLE 25 MV PILOT SOLENOID

Figure 22-25 sho,vs v.rhat occurs ,vhen the pilot is lit and prior to a call for heat. This part of the system is electrically active, supplying 120-V povver to the control transformer. The safety svvitch is closed and the po,-ver moves dovm to the

step-do,vn transforn1er, also active and supplying 24 volts to the control circuit. The thermocouple generates 20 to 30 millivolts DC to energize the pilot solenoid ,vhen exposed for a pilot fla1ne for at least 60 seconds.

SEQUENCE OF OPERATION 22.1: MAIN GAS VALVE The regulation of gas (step s of the generic sequence of op­ erations listed earlier) to the main burner is accomplished with the main gas valve. Use Figure 22-26 as you study the following sequence of operations:

O At point 1 the thermocouple is heated by the pilot light.

The flame generates a DC millivolt signal that energizes the pilot valve solenoid. The gas valve can now open when energized by the 24-V signal.

O At point 2, the thermostat closes, sending the 24-V

e

signal (see yellow highlighting) to the gas valve.

When the thermostat closes on temperature drop, the gas valve at point 3 is energized through the 24-V control circuit. In this circuit is another switch, the high limit switch, which needs to be closed. The gas continues to flow through the main gas solenoid valve as long as current is allowed to flow.

GAS HEATING SYSTEMS

O When the thermostat is satisfied at point 2 and opens

at point 4, the electrical flow through this circuit is interrupted and the main gas solenoid closes, cutting

407

off the flow of gas and extinguishing the main burner flame. The pilot continues to burn as long as the gas is provided to the furnace.

SAFETY S\VITCH &FUSE

FAN CONTROL

BLOWER MOTOR

1------------ 120 VOLTS------------

STEP DOWN TRANSFORMER

,________ 24 VOLTS ________,, T'STAT

0

HIGH LIMIT

0

GAS VALVE

THERMOCOUPLE

�---- 25 MY ------1..,. PILOT SOLENOID

Figure 22-26 When the t'stat in the 24-V control circuit closes, it energizes the gas valve and allows gas to flow to the burners. The

fan switch will close in about a minute of operation as the heat exchanger heats. This starts the blower.

Another S\vitch that n1onitors the fla1ne, indirectly, is the high li1nit control (step 8). This control senses heat in the heat exchanger and opens on rise to cut the flovv of electricity to stop the flovv of gas, only if the exchanger tem­ perature is too high. It acts as a safety control to monitor the 1nain gas valve and main burner flame. If, for instance, the flow of air over the heat exchanger is not enough to

keep thi.s s,-vitch closed, the high limit \ViJl open on te1nper­ ature rise and shut dovvn the main burner. The high limit may also be combined ,-vith another svvitch and act as one control, cal1ed the "Fan & Limit." The co1nbo svvitch will control the operation of the fan \•vhen the heat exchanger gets hot and interrupt the gas flo\V if the heat exchanger gets too hot.

408

UNIT22

SEQUENCE OF OPERATION 22.2: BLOWER OPERATION

O The fan switch closes at point 2 when the exchanger reaches its temperature setpoint. G The closed fan switch will operate the blower at point

In combination, the fan or blower is operated (step 9 of the generic sequence of operations) with another set of con­ tacts to turn the blower on when enough heat builds up in the heat exchanger. It also turns off the blower when the heat exchange temperature drops. The blower operation is highlighted in Figure 22-27 and explained here:

3. The fan switch at point 2 opens when the gas valve

has closed and most of the heat has been purged from the heat exchanger.

O When the gas valve is energized at point 1, it begins to warm the heat exchanger.

SAFETY SWITCH &FUSE

•

FAN CONTROL

BLO\VER l'vfOTOR

1i-.-----------120VOLTS----------...-

STEP DO\:Y'N TRANSFORMER

I

.._______ 24 VOLTS-------, HIGH T LIJ\.1I

T'STAT

GAS VALVE

I .

THERl\1OCOUPLE

'rMV _:,

.

PILOT SOLENOID

Figure 22-27 This diagram highlights the final stage in the heating operation. When the fan control switch gets warm enough to close, the blower begins to operate on medium or low speed. The high-speed connection (one of the two unwired connections) will be used for cooling operation if needed.

GAS HEATING SYSTEMS

409

Figure 22-28 When the thermostat is satisfied, the control circuit is de-energized and becomes inactive. The gas valve closes and the gas to the main burner is shut off. The pilot continues to burn. The blower is still removing heat from the heat exchanger.

SAFETY SWITCH &FUSE

FAN CONTROL

BLO\VER MOTOR

------------- 120VOLTS

-------------+-1

STEP DO\VN TRANSFORJ\1ER

•-------- 24 VOLTS ------� T'STAT

HIGH Lll\.11T

GAS VALVE

THERl\.1OCOUPLE

PILOT SOLENOID

As sho·wn .in Figure 22-28, ,.vhen the thennostat is satisfied, the control circuit is de-energized and becomes inactive. The gas valve closes and the gas to the 1nain burner is shut off. The srune thing \vould happen in this circuit if the thennostat remained closed ( calling for heat) and the high limit switch opened. This is because both S\vitches are in series in this circuit. If either switch opens, the gas valve is de-energized and there is no gas flo\V. The rise in space temperature satisfies the t' stat and the main burner flame is turned off. When the thermostat has been satisfied, the fan control ensures that the residual heat in the heat exchanger has been 1noved to the living space. But, there is still a sn1all fla1ne; the pilot is shown in Figure 22-29 and the blo\ver shuts off ,-vith the fan control open. The pilot should not go out. Instead, it should ren1ain burning, ,,vaiting for the thermostat to call for the main gas valve and light the 1nain burner once again. If, by chance or by fault, the pilot goes out, the pilot solenoid valve ,..,rill not have enough

current to hold the valve open. At that point the valve \Vill close, sensing that the flame has been extinguished.

22.14 HIGH-EFFICIENCY OPERATION As gas heating systen1s evolve fron1 lo,-v-efficiency, standard gas-burning appliances to n1ore efficient models that transfer heat to the air more effectively, more electrical devices have been added. Since this is an electrical book our emphasis ,vill be on the electrical components. Systen1s that are 80% efficient ,.vill have an ignition sys­ ten1, vent fans, and integrated circuits to monitor the various pressure sv.ritches and sensors. Each of these systems and indi­ vidual devices helps the unit burn gas more efficiently. More usable heat is able to be generated fron1 the ra\v gas and trans­ ferred into the living space. There is a trade-off of efficiency

410

I

UNIT 22

SA.FETY SWITCH &FUSE

FAN CONTROL

BLO\VER l\lIOTOR

---------- 120 V OLTS --------�

STEP DO\VN TRANSFORMER

•------ 24 V OLT S -----M T'STAT

HIGH LIMIT

GAS VALVE

THERMOCOUPLE -- -- 25 JVIV ___,.., PILOT SOLENOID

Figure 22-29 When the heat exchanger cools down, the fan control opens, turning off the blower motor. The unit is ready to start again when the thermostat senses a drop in temperature and begins the cycle again.

and price. Gas heating syste1ns that are more efficient generally cost more than lo\ver efficiency units. It is expected that the higher cost is offset by lo,-ver long-term gas bills. The ,viring diagrams for 80 AFUE and 90 AFUE sys­ tems appear very similar. Both have heat exchangers that have been lengthened, Vl hich causes the hot exhaust gas to travel longer distances. This design allo\vs for longer heat ex­ changer contact with the ail' and, thus, n1ore heat transfer. What is also interesting is that the exhaust gas is forced to travel do,¥n\vard in the heat exchanger so that the part of the exchanger that is the coolest (near the point where the vent motor is attached) is where the air returned from the living space is first blo,-v11. Th.is air is the coolest and tends to cool the exhaust gas to its lo·west temperature, thus extracting the last little bit of heat for the living space. A similar general operating sequence listed in the previ­ ous section is found in high-efficiency heating syste1ns: 7

l. The thermostat closes because the room temperature has dropped or the ten1perature has been adjusted to a lo,\rer ten1perature.

2. The control voltage is sent through the thermostat to start the furnace operating. 3. The gas valve is energized. It opens, allowing gas to start the ignition process. 4. Sense that a flan1e is established. 5. Regulate the supply of fuel and air mixture. 6. Nionitor combustion through safety controls. 7. When the heat exchanger ,¥arms, the blo,-ver n1otor n1oves heat to the living space. 8. The thermostat opens because the air has ,,varmed to its setpoint. 9. The gas valve doses and the burners extinguish. 10. The blo,¥er shuts do\vn after the heat exchanger cools to around 100°F. This takes about 1 or 2 1ninutes after the burners shut dO'\Vn. The signal from the thermostat is received fron1 R to W, as highlighted in blue in Figure 22-30A (found at at the botto1n of the diagram). At point l, the IFC (integrated fur­ nace control) begins the heating cycle. The IFC is a circuit board. The inducer vent motor at point 2 is started through the dosed limit s\vitch TCO-B at point 3 to pre-purge the combustion chan1ber to ren1ove any unburned fuel or vapor. After the vent motor has operated, the pressure s,vitch closes \vhen it senses negative exhaust pressure in the con1bustion area. The IFC also checks to see if there is enough pressure drop to safely exhaust combustion gases by ensuring the PRESSURE SvVITCH at point 4 has closed. \1Vhen pressure drop is sensed, the pressure svvitch closes, sending the signal to the IFC. The pressure s,¥itch is connected in series ,vith the limit s,-vitch TCO-A and the MANUAL RESET FLAME ROLLOUT SWITCH at point 5. These s\vitches w"Ould open if the temperature of either s,vitch becan1e higher than their rating. At the beginning of the cycle, these two temperature s,-vitches should be dosed because they are cool.

TECH TIP The rollout switch is sometimes a fuse-type safety switch. This means that if the switch is open, it needs to be replaced. Fuse-type safeties cannot be reset. Some, on the other hand, can be manually reset. Rollout switch temperature limits are set by the manufacturer. Always replace the rollout switch with the manufacturer's direct replacement.

At the end of the pre-purge cycle, all three S\Vitches must be closed (limit S\Vitch, rollout s,-vitch, and pressure switch) before the IFC (integrated furnace control) turns on the HSI (hot surface igniter) as seen at point l in Figure 22-30B. The gas valve at point 2 opens to begin the ignition process. At this time gas is flowing to the con1bustion or burner area. v\Then the gas hits the hot surface igniter (HSI), the gas \vill ignite to produce a flan1e. The FLAME SENSOR, at point 3, must sense the presence of a flame by allo,-ving

GAS HEATING SYSTEMS ,-------Wll------1=:i-...

411

R..AME SENSOR

WH/5 � �----------BK/5------ ==> ==> OPP ON I C•r JITIAT-11 TIAC-11 XF� -11 IIUM-11 UNE H _ I c:::, c:::, c:::, c:::, - _ _ _ ...I I c::::::I1 c:::, I IND-H BK/ 6 HUM-II g 2 c::::::II '-------BK/ 5-+--------ION-H �-H 3 c::::::II §:' -� I '-------WH/6-+--------IND-NI ==> S-1 ---= -----WH/5-+--------IGN-N XFM R-H OR-H -----o, =-1--WH-----+, f--' � CC COOL "OPP" IIEAT "OPP" DELAY ,±::::;::::::::::;:::::;;:::::::;DELAY SW2 SW3 DELAY ----� ---RD/I �SWI DELAY ON OFF 60SEC '-../ '---" INTEGRATED FURNACE .-ON 0'-1 100 SEC• - BL/ I YL-++-� ON 0SEC* '9) CONTROL (IFC) OFF ON l40SEC �-++-�,�,) OFF SO SEC OFF OFF 180 SEC RD I I--++--. II O II ' I ' GR .... l-++-� '' � ' ' •FACTORY SETTING 6) --. BL J;;i ij �ll!(!i......

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FROM DWG. D342775 REV. I

Figure 22-30A The 24-V signal is received from the thermostat at the R and w terminals as highlighted in blue (bottom right side). The vent motor is operated to pre-purge unburned gases and vapor from the combustion chamber. The limit switch TCO-A and flame rollout switch must be closed in order to "prove" the vent motor operation. The pressure switch will close next to finally prove vent motor operation.

the conduction of a small amount of DC po1,ver through the flame and back to the IFC, as highlighted in Figure 22-30B. As seen here, if the IFC can detect the presence of this small po,\rer source, the flame is proven and the combustion cycle proceeds. If not, the IFC turns off the gas. Depending on the manufacturer and 1nodel, the IFC may be programmed to attempt to relight the burner or it may go into the safety lockout mode (ahvays check the n,anufacturer's literature for operation).

The IFC is preprogram1ned (see s,-vitch setting). The blow·er in Figure 22-30B, point 4, is timed to turn on ,vhen the heat exchanger is ·warmed. The blower moves \.Varmed air from the heat exchanger to the living space. At the end of the cycle, the thermostat opens and the heating system starts the shutdO\VI1 cycle. The gas valve is shut and the blower contin­ ues for a predetermined amount of time to ensure that the heat exchanger is cool and the warmed air is driven in the conditioned space.

412

UNIT 22

3

JUNCTION BOX

------ WII--.......c=:i-... FLAME SENSOR

l}HSIJ 1

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"IMPORTANT: INTEGRATED CONTROL IS POLARITY SENSITI E. V HOT LEG OF 120\1 POWER SUPPLY MUST BE CONNECTED TO TIIE BLACK POWER LEAD ASINDlCATED ON WIRING DIAGRAM.

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FROM DWO. D342775 REV. J

Figure 22-30B

The flame sensor detects the flame, allowing a small amount of DC power to flow to the integrated furnace control (IFC).

22.15 BASIC TROUBLESHOOTING PROCEDURES Follo"\-v these basic procedures when checking gas heating systen1s: 1. Check for power. This basic check needs to be n1ade routinely before anything else is investigated. Ah\l'ays ensure that the correct line voltage is present. Figure 22-31 gives an exa1nple of how· to find the correct 120-V polarity.

2. Check for povver in the control circuit. Sometimes this basic check and the first basic check can be done at the sa1ne time. If 24 volts is 1neasured at the thermostat, then it can be assumed that the correct line voltage is present. If any deviation fro1n 24 volts is measured, the line voltage needs to be checked. 3. Check that the thermostat is set to call for heat. If not, set it a fev11 degrees above the room te1nperature. 4. Check that all pO"\-ver s,-v.itches are on and all fuses are good.

GAS HEATING SYSTEMS

Figure 22-31 This is a way to check for

------ INCOMING POWER

power polarity to a 120-v gas furnace. If the voltage readings are different than those shown here, there is most likely a reverse polarity issue.

•'/'

------M

.METER READS 0 VOLTS

METER READS 120VOLTS

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5. Check that the blower door switch is closed. 6. If the furnace had previously been operating, check for high temperatures that n1ight affect the safety controls or the safe operation of the furnace. Has the furnace been operating? Does the furnace or vent pipe feel ,-varm? 7. Check that furnace filters are dean and there is adequate airfl.o,-v. 8. Check for obstructions in the flue. This is typically a visual test and ,vill require ren1oving the vent pipe and going to the vent rain cap, removing the cap, and doing an inspection. After these basic checks have been n1ade, advanced trou­ bleshooting can proceed.

22.16 TROUBLESHOOTING OF HIGH­ EFFICIENCY SYSTEMS Many high-efficiency gas heating systems have the advan­ tage of having an electronic monitoring systen1 built in to the circuit board. This 1nonitoring system has a visual dis­ play of LEDs that provides the technician ,,vith an additional tool to use in troubleshooting. The nun1ber of flashes and the speed of the flashing indicate the type of trouble that was recorded by the circuit board. After speaking ·with the cus­ tomer and conducting the eight basic checks listed above, you should consult the circuit board troubleshooting codes sho,-vn in Table 22-5 before 1nanipulating or checking any other part of the syste1n. The electromechanical components of a high-efficiency gas furnace are similar to those of a lo,v-efficiency unit. Motors, relays, and solenoids all operate the same and

THIS JS THE COMtv10N OR NEUTRAL LEG

Table 22-5 Fault LED Flash Code Definitions Flash codes from a circuit board are used to troubleshoot a gas furnace. Not all flash codes are the same for a manu­ facturer and may be different among manufacturers.

Integrated Furnace Control Error Flash Codes Flashing Slow-

Normal - No call for Heat

Flashing Fast-

Normal - Call for Heat

Continuous ON-

Replace IFC

continuous OFF-

Check Power

2 Flashes -

system Lockout (Retries or Recycles exceeded)

3 Flashes -

Pressure Switch Error

4 Flashes-

Open High Limit Device

5 Flashes-

Flame sensed when no flame should be present

6 Flashes-

115 Volt AC power reversed or Poor Grounding

7 Flashes-

Gas valve circuit error

8 Flashes-

Low flame sense signal

(Trane-X341011P14.PDF; courtesy Trane corporation.)

typically ·with the same type of p0\\7er applied (120 and 24 volts). Circuit boards assist in troubleshooting, but ,-vhen a circuit board is bad, the technician 1nust be able to recognize the sympto1ns. Circuit boards usually fail completely. This

414

UNIT 22

1neans that the systen1 does not respond, even though the right voltage is applied. Voltage or pov.1er is considered to be one type of "input" to the circuit board. Other inputs might be temperature or pressure sensors. The output of the board is usually considered to be po\ver to other devices like the gas valve and the ignition syste1n. If the technician checks all of the inputs and outputs of a circuit board, the operation of the circuit board can be deter­ mined. For example, if the circuit board is not providing an output to open the gas valve, but the inputs are correct, the board is considered to be bad. Inspecting a re1noved board from the circuit can sometimes help to confirm that the board is bad. A board that has burned out will have a burned sn1ell. A crack in the board can be determined visually by holding it up to a light source. Since the circuit board is one of the most expensive components to replace, it is important for the technician to verify that the board is bad before re­ placing i.t. Because there are more components to check, the tech­ nician n1ust n1aintain a n1ental image of the syste1n opera­ tion. As discussed earlier, high-efficiency system operation is a little more complicated than lov.1 -efficiency operation. To help technicians, a manufacturer n1ay include a trou­ bleshooting flo--wchart in the troubleshooting section of a unit's installation manual (see the Figures 22-32A through 22-321 series for samples). The tlo\Vchart begins with an extension of some basic checks, such as checking for line

voltage and following the operation into the system. Notice that, very quickly, the technician observes the flashing LED to determine the fault code. The flowchart is built on the flash code of the LEDs. Each code has a different flowchart page. A service technician 1night use the Figure 22-32B flow­ chart in the follov.1ing scenario: A customer cornplains that there is no heat. The technician listens to the customer and determines that the custo1ner was able to reset the furnace by cycling the thermostat. No,�, turning the thermostat on and off has no effect. The technician does all eight basic checks and does not find anything unusual. The furnace attempts to start, but does not ignite. The LED on the circuit board is flashing tw·ice. A re­ vie\V of the flo,-vchart in Figure 22-32B confirms that two LED flashes 1nean the proble1n seems to be a cycle lockout. Starting with that part of the troubleshooting flo,-vchart, the technician disconnects electrical po,.ver to the furnace and connects a manometer to test for gas pressure. The inlet gas pressure \Vas not above 14"WC; instead it ·was I I "WC (liquefied petroleum or LP furnace). The LP gas pressure is good therefore the flovv chart switches to "Yes". The next step is to check the alignment of the hot surface ignitor or ignition source. Does the ignitor have 120V ap­ plied ,vhen it calls for ignition. Carefully clean the HSI if the silicon nitride type. Align back into the burner gas stream.

GETTING STARTED

NO

Is high volwge power supplied to the unit?

Repair high voltage connection to unit.

YES Close and hold door switch

ls the lFC LED flashing?

YES What is the fault light tlash code? See FAULT LED flash codes page

NO

ls 24VAC low voltage present from 1ransfom1er and fuse good?

YES

Arc connections and wiring in working condition?

YES

Replace lFC

NO Repair low voltage wiring, replace transfom1er. or fuse as needed

Repair connection,

Figure 22-32A This type of flowchart is typically found in the troubleshooting section of an installation manual. It is not intended to be a troubleshooting flowchart for all gas furnaces. consult the manufacturer to obtain a flowchart for a particular unit.

GAS HEATING SYSTEMS

415

DEFINITION RETRY Lock Qui = 3 unsuccessful tries ror i1mi1ion within a sinl!le call ror heal ' Flame has never been sensed

2 Flash Fault LED

RECYCLE Lock Out= IO recycles within a single call for heal. Flame is sensed & then lost

Disconoecl elec1rical power to funlllce. Connect manometer t.o inlet gas pressure connector

ls inlet gas pressure above 14" WC?

YES

Correct inlet gas pressure Check opera1ion

NO Cycle power to furnace and call for heat

NO

Is outlet gas pressure -3.5'' WC (NG) -1 l.O" WC (LP)'?

NO

YES Clean and align burners correctly ensure burner crossovers are clear of debris. Check operation

Adjust manifold gas pressure to -3.5" WC (NG) -11.0" \VC (LP) Check operation

YES NO

o all trumers ignite will1in 5 sec--� exchanger stay consistent? Check operation

YES Replace roll out �witch Check operation

GAS HEATING SYSTEMS

DEFTNffiON: Flame is sensed when il shot1ld not be sensed.

5 Flash Fault LED

Disconnect electrical power to furnace

Turn off gas supply! Remove gas valve

Are there signs ol moisture or debris in the inlet gas screen?

YES inspect gas supply for leaks imd have gas supplier check gas quality

Install drip leg per national fuel gas code and installation instructions

NO

Is there a drip leg installed mi inlet gas piping per installation instructions'/

YES Using a back-np wrench, install new gas valve Check operation

Figure 22-32F

NO

419

420

UNIT 22

T DEFTNT TON: Ground Fault- Tncoming or chassis round connection is 1101 sensed ::, Polarity Fault- TncomiJJg high voltage wiring is reversed Line voltage too low- Line voltage must not be below 97VAC

Reverse 120 VAC power leads to furnace wiring

Reconnect power Check operation

6 Flash Fault LED

Connect volt meter 10 white incoming neutral wire and green earth ground

Ts there a YES Disconnect ocs meter NO !-'II--; incoming elec trical�--< read ~120 VJ\C?';>--,� voltage greater th.an lOVAC? power to furnace

NO Connecl voll meler 10 black incoming and �-chassis ground at burner box

Disconnect NO Does meter Correct eat1h ground. , __ _, incoming electn· c·al ---< read ~ 120 VAC? Check operation power to fu rnace

'YES Disconnect incoming elecrrical power to furnace

Check/corred all ground connections wilhi11 furnace for continuity

Check operation

Figure 22-32G

NO ­ -

YES

Correct neutral an ground problem. Furnace must. be on a dedicated circuit

GAS HEATING SYSTEMS

Figure 22-32H

421

7 Flash Fault LED

DlFlNlTlON: External gas valve circuit error (24 volts is present when it should not be present)

Turn comfo1t control to "OFF' position

Is 24 VAC nominal voltage present between red lead at gas valve connection to chassis ground?

YES

Correct wiring Check operation

NO Rephtce IFC

Figure 22-321

DIFINITION: The flame sense current is less than l micro-amp de

8 Flash Fault LED

Disconnect electrical power 10 the fmnacc

Connect volt meter leads in se1ies with name sensor

Cycle power 10 furnace and l'll 11 for heal

ls tlamc sensor Correct flame NO I�--< located COITCCtly'/ sensor Joe.al.ion Sec figure

YES Check Replace name '""'----I operation sensor

YES

i--�

Meler mus! be set on de micro-amp scale

Is flame current measured less than 1.0 micro-amp DC?

NO Flame sensor is good. Check wiring and/or connections.

,-�0.71

0.51

0

0

0

1.645

HOT SURFACE IGNITER

FLA�1E SENSOR

422

UNIT 22 Turn the FAN switch 10 "ON" at the tbenuostar

Furnace PSC fan motor - N'o Air flow

NO

Check for dirty air filter, duct work damage or restrictions around the air handler coil and repair as needed

YES

Ts the fan wheel running?

NO s the high voltage power supplied to the unit?

Repair high

NO

'>-------"� voltage connection

to unit

YES

Is 24 VAC measured between '"R" (transformer hot) and "B/C" (transforn1er common) at the low voltage field connections?

NO

Ts Lhe proper line voltage prese(lt at Lhe Lransfo1mer?

NO

YES

Repair wiring between incoming power supply and transformer.

between "G" and "B/C'' at the low voltage

NO

YES

Ts line voltage measured between motor common and applied speed tap at IFC? CIR-N and HEAT-H

YES YES >--·< Ts fuse blown? >--+iReplace fu�e.

NO Replace transformer.

Check Lhem10s1a1 and wiring to tl1ermostal

NO

Replace the lFC

YES

ls microfarad reading of fan motor run capacitor within 10% of rated value?

NO

YES

Replace nm capacitor.

Replace fan motor and run capacitor.

Figure 22-33 This troubleshooting flowchart is designed to guide a service technician through the check sequence for a PSC blower motor. This chart can be used for both low- and high-efficiency gas heating systems.

There is no flash code for "No Air." If the basic checks are used before the troubleshooting process, blow·er and air trouble ·will be found. Both lo,,v- and high-efficiency syste1ns experience air problems. High-efficiency systems may have an electrically conm1utated motor or a standard PSC (permanent split capaci­ tor) 1notor. TI1e Figure 22-33 tlov.,chait couJd be used for both lo,.v- and high-efficiency gas heating systems that use PSC motors.

22.17 ADDITIONAL REVIEW OF GAS FURNACE OPERATION No,v ,ve con1pare the differences and similarities of a n1id­ efficiency gas furnace using Figures 22-34, 22-35, and 22-36. (For a con1plete, enlarged viev.1 of these figures, see Electrical Diagra1n ED-10, ,.vhich appears with the Electrical Dia.grains

GAS HEATING SYSTEMS

-

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TO I 15VAC FIELD DISCONNECT NOTE#2 EQUIPMENT GROUND L2

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Figure 22-34A This is the ladder diagram embedded in Electrical Diagram ED-10. It is extracted from the large diagram so that it will be easier to trace. It is useful to have a ladder diagram and wiring diagram when tracing or troubleshooting a circuit.

424

UNIT 22 NOTES: IF ANY OF THE ORIGINAL EQUIP.MENT \VIRE IS REPLACED USE WIRE RATED FOR 105 °C. USE ONLY COPPER \VIRE BETWEEN THE DISCONNECT SWITCH AND THE FURNACE JUNCTION BOX (JB). THIS \.VIRE .tv1UST BE CONNECTED TO FURNACE SHEET METAL FOR CONTROL TO PROVE FLA.tvlE. SYMBOLS ARE ELECTRlCAL REPRESENTATION ONLY. SOLID LTNES INSIDE PCB ARE PRINTED CTRCUTT BOARD CONDUCTORS AND ARE NOT INCLUDED IN LEGEND. REPLACE ONLY \VITH A 3 Alv1P FUSE. INDUCER (IDM) 1/fOTOR CONTAINS INTERNAL AUTO-RESET THERMAL OVERLOAD S \VITCHES (OL). L2 CONNECTIONS ARE INTERCHANGEABLE \VITHIN THE L2 CONNECTOR BLOCK. BLOWER MOTOR SPEED SELECTIONS ARE FOR AVERAGE CONDITIONS, SEE INSTALLATION INSTRUCTIONS FOR DETAILS ON OPT1Mill1 SPEED SELECTION. 10. FACTORY CONNECTED WHEN BVSS (CHll'v1NEY ADAPTER ACCESSORY KIT) IS NOT INSTALLED. I l. FACTORY CONNECTED WHEN LPGS IS NOT USED. 12. IGNlTION-LOCKOUT \VlLL OCCUR AFTER FOUR CONSECUTIVE UNSUCCESSFUL TRIALS-FOR-IGNITION. CONTROL WILL AUTO-RESET AFTER THREE HOURS. 13. BLO\VER-ON DELAY: GAS HEATING 25 SECONDS, COOLING OR HEAT PU1vlP 2 SECONDS. 14. BLO\VER-OFF DELAY: GAS HEATING SELECTIONS ARE 90, 120, 150 OR 180 SECONDS, COOLING OR HEAT PUMP 90 SECONDS OR 5 SECONDS WHEN DHUl'vf JS ACTIVE. 15. BLVv1v1 IS LOCKED-ROTOR OVERLOAD PROTECTED BY REDUNDANT ELECTRONIC CONTROL CIRCUITS. 16. INDUCTOR USED \VITI-I 3/4 HP, l HP BL\�1v1.

l. 2. 3. 4. 5. 6. 7. 8. 9.

Figure 22-34B

package that accompanies this book.) 1-Iere is a breakdo,vi1 of the figures: ■ Figure 22-34 shows a view of the ladder diagram in Electrical Diagram ED-10. ■ Fi re 22-35 sho,-vs a vie,,v of the connection diagram in gu Electrical Diagram ED-10. ■ Figure 22-36 is the legend for these diagrams. The leg­ end ·will be important in identifying the components bet\,veen the tw-o diagran1s. The high-efficiency gas furnace can be challenging to a student as ,veil as a technician. Before revie,-ving the follo,,v­ ing sequence of operation for a gas fi.1rnace, a fe,..v in1portant points need to be clarified. You must understand that the

blow·er door must be installed or the door switch depressed for po,ver to be conducted through the blower door interlock s,-vitch. The door switch is sometimes bypassed to allo' C:.N C:.N SIZE � - � c:.w W� W� W� W �� � � c:.w � c:.w -=:J -=:J -=:J -=:J 070 5252 DEF. 700 875 10501 1225 1225 1225 525 875 DEF. 7002 1050 1225 14001 1400 090 110.135. DEF. 8752 1050 1225 1400 17501 2100 700 155

�'.:

Figure 22-35A This is the connection diagram extracted from Electrical Diagram E0-10.

BLWM LI

PL14

G)

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(/)

:r: m

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G) (/)

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-i

m

426

I I I I I I I I I I I I

1

I I I I I I I I I

UNIT 22

LEGEND NC ACR ACRDJ BLWM BVSS CF COMMR CPU DHUM DSS EAC-1 EAC-2 FRS FSE FUSE GV GVR HPS HPSR HSI HSIR HUM HUMR IDM IDR II-I/LOR

AIR CONDITIONING (ADJVS'fABL£ AIRFLOW -Cl'M) AfR CONDITIONING RELAY. SPST (N.0.) AIR CONDITIONING RELAY DEFEAT JUMPER BLOWER MOTOR (ECM) BLOCKED VENT SAPETY SWITCH. MANUAL RESET, SPST(N.C.) T CONTINUOUS PAN (ADJUS ABLE AIRFLOW-Cl'M) COMM.UNI.CATION RELAY, SPOT MICROPROCESSOR 7 CIRCUITRY DHUM CONNECTION (24VAC ) DRAFT SAFEGUARD SW.. AUTO-RESET. SPST (N.C.) ELECTRONIC AIR CLEANER CONNECTION (115VAC 1.0 AMP MAX.) ELECl'RONIC AIR CLEAl'.JER CONNECTION (COMM.ON) FLAME ROLLOUT SWITCH, MAN. RESET, SPST (N.C.) FLAME-PROVING SENSOR ELECTRODE FUSE, 3 AMP, AUTOMOTIVE BLADE TYPe. FACTORY INSTALLED GAS VALVE GAS VALVE RELAY, OPST(N.0.) HIGH-HEAT PRESSURE SWITCH, SPST(N.0) HIGH-HEAT PRESSURE SWITCH RELAY, SPST(N.C.) HOT SURFACE IGNITER (I 15VAC) HOT SURPACE IGNITER RELAY, SPST(N 0.) 24VAC HUMIDIFIER CO�"NECTION (0.5 AMP 'MAX.) HUMIDIFIER RELAY, SPST (N.0.) INDUCER DRAFT MOTOR 2-SPEED, SHADED POLE INDUCER MOTOR RELAY, SPST (N.0.) INDUCER MOTOR SPEED CHANGE RELAY, SPOT

ILK IND LED LOPS LPS LS 1,2 PCB PLI PL2 PU PL4 PL7 PL9 PLJO PLl 1 PL12 PLI � PLJ4 SWl-1 SWJ-2 SWJ-3 SWl-4 SW1-5 SW1-6 SWJ-7,8 SW4-I SW4-2&3 TR, 1,2 PCB PL! PL2 PU PLA PL7 PL9 PLIO PLII PL12 PLl3 PL14 SWl-1 SWl-2 SWl-3 SWl-4 SWl-5 SWl-6 SWl-7.8 SW4-1 SW4-2&3 TRAN

BLOWER DOOR lNTERLOCK SWITCH. SPST (N.0.) TNDUCTOR (NOTE #7) LIGHT EMITTING DIODE FOR STATUS CODES LOW GAS PRESSURE SWITCH, SPST (N.O.) LOW-HEAT PRESSURE SWITCH, SPST(N.0.) LIMIT SWITCH. AUTO-RESET, SPST(N.C.) PRINTED CIRCUIT BOARD 12-ClRCUlT CONNECTOR 4-CTR.CUlT HST & TOM CONYECTOR 4-CIRCUIT ECM BLWM CONNECTOR 4-CIRCUlT MODEL PLUG CONNECTOR 4-CJRCUIT COMMUNJCATLON CONNECTOR 2-CIRCUlT OAT CONNECTOR 2-CIRCUIT HSI CONNECTOR IDM CONKECTOR(3-CIRCOlT) 1-CTR.CUIT INDUCTOR SPLICE CONNECTOR 16-CIRCUIT ECM BLOWER CTRL. CONNECTOR T 5-ClRCUI ECM BLOWER POWER CONNECTOR MANUAL SWITCH, STATUS CODE RECALL. SPST (N.0.) MANUAL SWITCH, LOW-HEAT ONLY, SPST(N.O.) MANUAL SWITCH, LOW-HEAT RISE ADJ. SPST(N.0.) MANUAL SWITCH, COMFORT/EFFICIENCY ADJUSTMENT, SPST(N.0.) MANUAL SWITCII. COOLING CflM/T'ON. SPST(N.O.) MANUAL SWITCH, COMPONENT TEST, SPST(N.0.) MANUAL SWITCHES. BLOWER OFF-DELAY, SPST(N.0. l MANUAL SWITCH, TWINNING MAIN (OFF)/SEC. (ON) FOR Fv'TURE USE TRANSFORMER, 115VAC/24VAC

•

0

JUNCTION TERMINAL CONTROL TERMlNAL FACTORY POWER WIRING (l 15VAC) FACTORY CONTROL WlRING(24VAC) FIELD CONTROL WlRING (24VAC) CONDUCTOR ON CONTROL

0 rh -{ f-

FIELD WIRING SCREW TERMINAL EQUIPMENT GROUND PLUG RECEPTACLE

Figure 22-36 This is the legend for Figures 22-34 and 22-35. The legend will help you understand what the components on the

diagram mean. The legend is the abbreviated language of a wiring diagram.

GAS HEATING SYSTEMS

427

SEQUENCE OF OPERATION 22.3: GAS FURNACE You will notice in the wiring diagram of Figure 22-37 that all of the 120-v components have a black (BLK) and white (WHT) wire going to them. Black for the "hot side" and white for neutral are commonly used colors for identifying

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10 DHU1v1I0 � c:, G 10 n CO!'vf � n 24V 10 C -�- \V 10 co -0

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R

BLO\VER OFF-DELAY JUMPER SELECT OR

10

10

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FAN

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--•• -• --

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.

-

180

0

corvr N
----,....___

• TESTffWTN

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PLl-8

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R0

-

DSS

FRSl

BVSS (WHEN USED)

Q' :

w NOTE#3

• FSE

/}------+----,---C:=::::)•PLI-3 COM 24V ....--41==:)• PLl-7 PCBNOTE#5

'-

Figure 22-38

I

In this diagram, the upper section is the high-voltage section. The part below the transformer is the low-voltage section.

430

UNIT 22

1

115V NEUTRAL

Ll

:---- M6

:tv17 �----l\18

'Wv-----H

H

SEC. SEC. SEC. SEC.

Q104 OFF 1-30 ON 30--90 Qll0 OFF 30--60 ON 10--30

Q105

'

.Ml''

'Wv

H'

Ml�

M2

H

Iv13 �

M4

M4

'Wv OFF 1-110 ON 1-110

:tvl6

:tvl2

' 0 '

M3 :� ' '

Figure 23-14 The Hor heater

connections are for the control voltage. Most sequencer control voltage is 24 volts. Notice that model Q113 requires a 240-V control. The M or main connections will supply high voltage to the blower or heat strips.

Ql03 & Qll3

1'.15� H,'

SEC. SEC. SEC. SEC.

445

H SEC. SEC.

'

'Wv

H

OFF 40--110 SEC. ON 1-20 SEC. *Qll3 OFF 15-65 SEC. ON 30--l0 SEC. *QI 13 HAS 240 VOLT HEATER

Ql03

together in parallel with the 24-V control ,-vired to the bot­ tom connections. The top two sections ·will operate two sets of heat strips. The bottom set of heat strips ·will operate hvo more sets of heat strips. The brass connection near the bot­ tom mounting place ,vill be energized by 24 volts to close the contacts in a staged manner so that not all the heat strips operate at the same time. Figure 23-14 shovvs the various electrical symbols used for a sequencer. The capital letter "H" is used to represent the control voltage connections, which are usually 24 volts. The letter "M" and a nun1ber follovving M represent the sequencer contacts' identification. As stated earlier, the sequencer uses a time-delay circuit, ,vhich is accomplished by heating a bi­ metal strip. When the bimetal is heated, it expands, extend­ ing a rod, closing contacts beh-veen the M connections. \'\Then the sequencer H coil is de-energized, it cools and the bimetal contracts and opens the M contacts. The design of the time­ delay bimetal heater creates 1nore time or less thne for the contacts to close and open. The information in Figure 23-14 show'S a sequencer n1odel nu1nber Ql0l. When the H coil is energized (point 1), it closes contacts between Ml and M2 (point 2) after a 1- to 20-second delay. The sequence contacts open, or turn off, after 40 to 110 seconds. Notice that model Ql04 closes the M contacts later, at 30 to 90 seconds, while opening the M contacts sooner, at 1 to 30 seconds. A com1non sequencer operation is that the first sequencer ·will bring on the first heat strip and blo,-ver. The first sequence will be the last one to open or go off at the end of the heating cycle. In summary, the first sequence be the first one on-operating the blo,ver-and the last one off. This ensures continuing blower operation until most heat strips have turned back off.

'"'ill

Using Figure 23-13 and the Q 105 diagram in Figure 23-14, let's see ho,-v this will ·work: I. When the thermostat calls for heat, both 24-V sequencer coils H are energized simultaneously. 2. When energized, the sequencer on the left Figure 23-13 vvill be energized first by the 24-V control voltage, ,vhich closes after a short tin1e delay. 3. Refer to Figure 23-14. The blo,ver and t,vo sets of heat strips ,-vill begin to operate. This is caused by the con­ tacts bet\veen Ml-M2 and M3-M4 closing. 4. The second sequencer ,vill close after a longer time delay and close contacts M5-M6. 5. All heat three heat strips and the blo,-ver ,vill be operating. 6. \!\'hen the thern1ostat is satisfied, it vvill de-energize all the H coils. 7. The second sequencer (Iv15-lv16) will open after a short delay. 8. The last heat strip that ,vas energized will turn off first. 9. The first sequencer H coil ,vill de-energize last. 10. The blovver and first heat strip will now· turn off. As sho,-vn in Figure 23-15, some sequencers close several sets of contacts to turn on multiple strips of electric heat. The sequencers are designed to operate in a tin1ed sequence. For example, the sequencer on the left ,-vill close very quickly once energized. It ,-vill operate the first heat strip and blovver. The middle sequencer will come on after a time delay. The sequencer on the right closes minutes after it is energized. Sequencers are made in many different styles. So1ne are solid state and vvork si1nilarly to PTC (positive te1nperature coefficient) relays. Others are designed and look silnilar to an overload or snap disk. It doesn't matter how they are con­ structed, each type of relay does the same thing.

446

UNIT 23

Figure 23-15 Note that there are three sequencers with the control tied together.

Other Types of Controls Silicone controlled rectifiers (SCRs), also called silicone gate controlled rectifiers, are another way of controlling po·wer de­ livered to electric strip heaters. The SCR is a solid-state device that can turn on and off very quickly. Because it is a "recti­ fier" (a device that only allow·s electrical flo·w to occur in one direction), nvo SCRs are used to control one electric heating ele1nent. The signal to the SCR comes from a circuit board. The way it generally works is as follows:

1. The thermostat signals the need for heat. 2. The circuit board receives the sign al and interprets it for the level of heat needed. 3. The circuit board sends both SCRs a pulse signal to turn on part of the AC sine ·wave. 4. As the sine ,-vave moves through zero volts, the SCRs turn off. By turning on only part of the AC sine wave, only a por­ tion of the applied voltage reaches the electric heating ele­ n1ent. The element only heats to the temperature that meets the heating need of the structure and satisfies the thermostat setpoint. \Vorking on electric heating syste1ns ,-vith SCR controls requires son1e knowledge of solid-state controls and atten­ tion to the manufacturer's recommendations. Ahvays read and understand the manufacturer's installation and service 1nanuals.

H, SEQUENCER COILS TIE TOGETHER

Figw·e 23-16 sho,-vs t\.vo com1non fuses, the plug-in fuse and the glass (Buss) fuse, used in a control circuit board. These types of fuses can also be found in the secondary side of a transforn1er. Figure 23-17 sho,.vs a circuit board ,vith the plug-in U-typ e fuse. Breakers or fuses of the correct amperage and voltage rating should be ·within easy access of the heating system. Typically, the breaker is the same rating as the maximu1n an1perage listed on the nameplate of the electrical heating unit. The installing contractor may need to interpret the amperage values of an installation to apply the correct size breaker. In some instances, a breaker of 115% of the unit's "minin1un1" amperage may be specified. A larger breaker should never be used. A breaker is designed to protect the equipment and ,,vire. A breaker of greater amperage ,-vill not turn off the elec­ trical supply in the event of overcurrent draw. A breaker that is too small ,vill turn off the po,-ver before the maxi1num cur­ rent is dra,\'Il by the unit. Next, \\'evvill discuss the fusible link and thermal overload.

23.8 OVERCURRENT PROTECTION In this case overcurrent protection sin1ply means a fuse, breaker, or fusible link or overload device used to protect the equipn1ent, a circuit in the equipment, or ·wiring. These terms are often used interchangeably because they have som .e similarities. In the case of breakers or fuses, they are nor1nally used to protect the ,,vhole unit from excessive current, but they can be sized to protect one component in the unit. You ,vill have overcurrent protection for the unit and you m . ay have optional protection for components like the trans­ former or circuit board.

Figure 23-16 Plug-in fuses are used to protect a circuit board from overcurrent conditions. A glass fuse can be used as a plug-in fuse or in a fuse holder. (Penny shown for size reference.)

ELECTRIC HEATING SYSTEMS

447

Figure 23-17 This is a circuit board for an air handler with an option for electric heat strips. Notice the 3-amp plug-in fuse located at the upper left side of the circuit board.

·-···· -.. •

-

...� " tJ

23. 9 FUSIBLE LINKS A fusible link (see Figure 23-18) is often wired in series,,vith an electrical heating element. The purpose of the link is to open ,vhen either high an1perage or high heat is encountered. The fusible link cannot be reset and .must be replaced if open. The cylinder is silver and has manufacturer information printed on its surface. The information may include temperature and amperage ratings. The link is a small cylindrical device that has one square end and one tapered end. The taper may be black or red, depending on the color of the 1naterial used in its n1anufacture. The link can be checked for continuity to detern1ine if it is open. Resistance should be zero ohms.

23.10 THERMAL OVERLOADS A thermal overload, where thermal refers to heat, is a safety device used to open a heating circuit in case of excessive heat. For example, excessive heat will be created by a lack of

Figure 23-18 This common fusible link is found in series with a heating circuit. It is used to protect the heating circuit from damage. If an overheating or overcurrent condition occurs, it will open and not reset. When this happens, the fusible link will need to be replaced.

448

UNIT 23

TE1\1PERATURE ADJUSTMENT

Figure 23-19 Thermal overloads on a commercial electric strip

heater. These heating elements are protected by two thermal overload devices. The overload is like an eye, watching over the heating element.

LOW VOLTAGE WIRE UPPER OVERLOAD

HIGH VOLT..!\GE \VIRE

Figure 23-21 This is an adjustable thermal overload. The

temperature can be adjusted to the appropriate safety temperature.

airflow if the blower 1notor stops or if the air filter or evapo­ rator coil is dirty. The thermal overload is usually a bin1etal device that opens when the air temperature rises. These devices are nor­ n1ally round and look like an eye. Figure 23-19 sho1,vs t\vo ther­ mal overloacb monitoring a large commercial electric heater. Figure 23-20 sho1,vs the backside of the two thennal overloads sho1,vn in Figure 23-19. Notice that nvo gauges of vvire are used to hook up the overloads. The upper overload is vvired in the lower amperage control circuit. The botto1n overload is con­ nected in series -.,,rith the heat strips; therefore, it must be ca­ pable of handling the higher amps that run through these heat strips. It has the larger, lo,ver gauge red vvire. Most thermal overloads are the automatic-reset type. This means that when the overload opens, then cools, it "''ill auton1atically close its contacts and allo1,v the heat strips to operate again. A thermal overload can also be designed \,\7ith a manual reset option. The manual reset 1neans that the tech­ nician ,\rill need to push a button on the back of the overload to get it to reset or dose. Finally, so1ne thermal overloads are adjustable. Figure 23-21 shows a picture of an adjustable thermal overload. This device allo,\7S a technician to stock one thermal overload on the service truck or at the office that can cover various temperature applications.

23.11 MISCELLANEOUS COMPONENTS Figure 23-20 This is the backside of the thermal overload.

Notice that two gauges of wire are used to hook up the overloads.

The electric heating system has other components necessary for its operation. The furnace ·will have a blo,ver assembly and possibly a circuit board. It may also have a filter rack,

ELECTRIC HEATING SYSTEMS

and a filter grille n1ay be placed in the return air duct system. It is also con1mon to find an evaporator coil in the electric furnace cabinet.

23.12 WIRING REQUIREMENTS Electrical supply wiring for electric heating systems is very important. Wire sizing 111ust conform to the National Electrical Code as ,,vell as local code require1nents. Be familiar vvith all applicable codes. Wiring is based on amp draw and, to a lesser degree, supply voltage. Electric heating units can draw significantly high amperage. The nameplate of all electric heating units ,,vill list the amp draw. In some cases the amp dra\.V is part of the unit n1odel nu1nber ( check vvith the 1nanufacturer for model number identification). Amp draw· charts are based on copper \Vire gauge. Some installations n1ay use aluminum vvire if it is permissible. Some manufacturers n1ay prohibit the use of alun1inum \-Vire. If alu1ninu1n is used, connections 1nay require the use of a special connection coating or anti­ oxidation material. Copper ,,vire does not require a special coating to be applied at connection points.

SAFETY TIP If electrical supply wire for an electric heating system is noticeably hot, there may be a problem with the size of the wire or the wiring connections or there may be a break in the wire insulation that is allowing oxidation breakdown of the wire (in the case of aluminum). If the technician suspects that the temperature of the wire is too high, a qualified electrician should be called to deter­ mine if there is a problem.

SAFETY TIP Electric wire used to connect heating elements is rated for temperature and amperage conditions. Be sure to use wire that is rated for the condition. Wire not rated for this condition may melt, causing short circuits and an electrical fire.

23.13 OPERATION A single strip of electrical heating element is easily oper­ ated, as in the case of baseboard or radiant panel heating. When multiple strips of heat are used, control of the sys­ tem becomes n1ore complicated. For purposes of explana­ tion, an electric furnace \\rill be used. Keep in mind that

449

other installations that use multiple stages of electric heat will generally operate in the sa1ne \Vay. An electric furnace vvith three strips of electrical heat­ ing elements and a t\-vo-stage thermostat is installed in a residential application. The first t,vo strips of electric heat are sized to hanc.Ue the residential heating load under nor­ mal conditions. If the outside ten1perature should drop to a point \'\There the first two heat strips are not creating enough heat, the temperature in the residence ,,vould drop, caus­ ing the second stage of the thern1ostat to call for additional heat. Here is a sequence of operation ,.vhen a thermostat calls for heat: 1. FIRST-STAGE HEATING OPERATION: The signal is received by the first sequencer and the blower relay. 2. The sequencer delays for approximately 30 seconds and turns on the first electrical heating element and blo\ver. If the fusible link and the overload are closed, the elec­ tric heating element begins to vvarm. 3. The first sequencer and second sequencer heaters are in parallel; therefore, they are both energized at the sa1ne time. The second sequencer ,vill begin its 60- to 90-second tin1e delay. At the end of the second sequencer's time delay, the second heating element is po,,vered and begins to warm. 4. The operating blower moves air across the heated elec­ trical elements, cooling the elements and ,varming the air to be distributed to the occupied space. 5. When the temperature of the room meets the set­ point of the thermostat, the thermostat opens the W circuit. 6. The control voltage signal is lost to the sequencers. The second sequencer turns off the second heat strip after a short time delay. Then the first sequencer turns off the first strip of heat after a longer delay. 7. When the first sequencer turns off, the fan control ""ill turn off the blo,,ver. 8. SECOND-STAGE HEATING OPERATION: If the first stage of heat (first t\vo heating elements and blo,ver) did not satisfy the thern1ostat setpoint and the temperature of the occupied space drops, the second stage of heat­ ing begins. The second stage of the thermostat ,vould close. This is normally labeled as W2 on the diagram or thermostat. 9. When the second stage of the thermostat closes, both the first and second strips of heating vvill already be operating. The third sequencer is then energized, delaying po,-ver to the third strip of heat for approxi­ mately 60 seconds. The third heating strip operates until the room temperature rises to turn off the sec­ ond stage of the thennostat W2. At this point, the third sequencer turns off power to the third heating elen1ent. When the roon1 ten1perature is met, the other heat strips are de-energized as described in steps 5, 6, and 7.

450

UNIT 23

23.14 EFFICIENCY CHECK An electric heating syste1n has the advantage of being easily checked for efficiency and proper airflo,-v. These systems do not have to factor in the efficiency of fuel conversion or the efficiency of the fuel burned. To check for proper airflO'w, the follovving procedure is used: I. Measure the amp draw of the operating heating ele1nent (or elen1ents), including the blo,\7er amperage. The sys­ tem should be fully energized for thi.s measurement. This can be done at the furnace disconnect. 2. Measure the operating voltage. 3. Measure the return air temperature. 4. MeasuTe the supply air temperature. This air tempera­ ture must be measured at three diameters of the ple­ num (at least), downstream of the heating elements. The temperature probe n1ust also be shielded from the radiant energy given off from the elements (if there is direct line of sight). The airflow must be mixed to get an accurate temperature measure1nent. One way to ensure the accuracy of the te1nperature measurement is to place the temperature probe past the first supply air elbo,\7 so the heat coining directly off the heat strips ,vill be n1i:x:ed. 5. The follo'--

Defective low-voltage transformer

Remote control center >-defective

>--

>--

>--

>--

-

Contactor coil open or shorted

Open .indoor thermostat

Liquid-line pressure switch open

Loss of charge

Open control circuit

I

�

>--

>--

>--

>--

>--

>--

-

I

1.;ompressor runs but cycles � on internal overload

Contaetor closed

Compressor power supply

Loose leads at compressor

Faulty start gear (1-PH)

Compressor stuck

-

Low snction low head

>--

Defective fan motor capacitor

Omdoor ran stopped

>--

Damaged reversing valve

Loose leads at fan motor

Loose leads at outdoor ran motor

-

Internal fan motor Klixon open

-

>--

>--

>--

Open shoned or grounded compressor windings

>--

Defecli.ve start capacitor

Dirty ftlters or indoor coil Indoor ran stopped or cycling on overload

Compressor internal overload open

Defective run capacitor

Compressor nms insnfficient heating

-

Restriction in discharge line Overcharge or noneondensables in system Low refrigeram charge

>--

>--

-

-

Fan motor burned out Defrost relay N.C. contacts open on circuit board

Defective nm capacitor (l-PH) Compressor bearings

>--

High-load condition

>--

Reversing valve jammed in midposition

-

-

Fan motor burned out

>--

Linc voltage too high or low

>--

>--

>--

-

High superheat Defective start capacitor

Figure 24-45 Heating cycle troubleshooting chart.

Fan motor contacts welded closed in defrost relay

Reversing valve did not shift

Unit not properly charged

>--

>--

I

Outdoor ran running

Reversing valve stuck

Restricted liquid line Piston restricted or is clogged

-

Undercharged

-

Outdoor coil dirty

-

Strainer restricted

-

01lldoor coil l1eavily frosted

-

Defective defrost thernmstat

Defrost - thermostat in poor physical contact. with tube

-

Defective circuit board

-

Bad elecu·ical connection anywhere in defrost circuit

I

-

Strip heaters not operating

-

Outdoor thermostat defective

>-

-

ODT selling too low Cap tube pinched or bulb not sensing true ODT Strip heater relay or contactor defective

Opening in power circuit l.o heater elements >-

-

Broken fuse link Broken beater element

-

Open (Klixon) over temperature them1o�tat

-

Defect.ive room thermostat (2nd stage)

HEAT PUMP HEATING SYSTEMS OUTDOOR COIL COOL

•• • • •

487

• INDOOR COIL REVERSING VALVE

COOL

FLOW IS :METERED

••••• •••• vVARtvI LIQUID

METERING DEVICE

FLOvV BYPASSES , .........,....., METERING DEVICE

Figure 24-46 use this diagram to answer Review Question 11.

OUTDOOR COlL

FLO\V BYPASSES METERING DEVICE

Figure 24-47 use this diagram to answer Review Question 12.

REVIEW QUESTIONS 1. Describe "v'hat is meant by the tern1 electromechanical and nan1e components that are considered to be electro1nechanical.

8. Name two ways to troubleshoot a reversing valve solenoid coil. 9. Nan1e five electrical components found in a heat pump that arc not found in a conventional air conditioning system.

2. Describe the function of a wiring diagram legend.

10. Briefly describe the defrost cycle operation.

3. Name six common heat pun1p components.

II. Identify the heat putnp cycle shown in Figure 24-46.

4. Explain how inside electrical components and outside electri­ cal components are connected to function as one unit.

12. Identify the heat p1unp cycle shown in Figure 24-47.

5. Describe the start-up and shutdown of one mode of operation or defrost. 6. Explain why a hard start kit is used and describe its operation. 7. Describe what benefits might be derived from having a micro­ processor ( circuit board) as part of a system.

13. Refer to Electrical Diagram ED-11. ls the reversing valve ener­ gized in the heating or cooling mode? 14. List five reasons for inadequate defrost.

15. What happens when you switch the heat purnp thermostat to e1nergency heat 1node?

488

UNIT 24

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DISCONNECT 1 I

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4

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Figure 24-48 use this diagram to answer Review Questions 21 and 22.

16. You are servicing a unit and realize that the defrost cycle is not long enough to clear the frost off the coil. How do you increase the frequency of the defrost cycle? 17. You are called to service a heat pump before the v.rinter season. lt operates in cooling mode, but will not shift to the heating mode when the thermostat is changed to heat. The R-410A pressure is 190 psi on the high side and 100 psi on the low side. What is the problem?

18. vVhen would a heat pump, rather than some other type of heat­ ing equipn1ent, be selected for installation?

19. True or false: The thermistor used in the defrost cycle measures pressure. 20. \·\That are the three refrigerant cycles used in a heat pump? 21. \!\'hat type of defrost system is used on the heat pump shown in Figure 24-48? 22. Does the heat pump diagran1 of Figure 24-48 show the outdoor section, indoor section, thermostat, or any combination of these?

UNIT 25

How to Start Electrical Troubleshooting WHAT YOU SHOULD KNOW After studying this unit, you will be able to: 1. Define troubleshooting.

2. State the steps of troubleshooting. 3. Describe a logical sequence for starting troubleshooting. 4. use the human senses to detect problems. s. Name seven types of troubleshooting techniques.

It is difficult to teach any type of electrical troubleshooting. The reason it is so difficult to teach and learn troubleshoot­ ing is because there are many problems that are not clear-cut. Is it an electrical problen1? Mechanical problem? Or a con1bi­ nation of both electrical and n1echanical? The technician cannot see electricity and must use electrical meters to narro,v do,vn and solve the proble1n. Technicians need to thoroughly understand how to use aU of their electric 1neters' functions in order to fully troubleshoot electrical problen1s. Another reason it is difficult to teach troubleshooting is because problem-solving techniques vary from person to person. In many cases there is 1nore than one way to solve a proble1n(s). The troubleshooting units in this book \-\rill offer different \.vays of solving these problems. Choose the process that works best for you. Next, problems can blend together. There can be more than one problem. Mechanical and electrical problems can occur simultaneously. A mechanical problem can cause an electrical problem. For example, a refrigerant-flooded com­ pressor ,vill reduce the lubrication of moving parts and the 1notor bearings ,vill ,vear out due to a lack of lubrication. The ,vorn motor bearings ,vill allo\V the motor rotor (the part of the motor that rotates) to drag on the stator (the station­ ary ,vindings). The dragging rotor ,vill short out the stator ,vindings and it \.vill appear to be an electrical problem. If the reason for the electrical failure is not corrected, the replace­ n1ent compressor ,vill soon face the same type of electrical failure, even though the original cause of the problem ,vas a flooded compressor. Finally, individuals learn differently. One person \vill learn and put into practice ,.vhat is presented in this unit. Another person ,vill read this material and totally ignore the value of using a logical approach to troubleshooting. Everyone ,-vants hands-on practice and experience. This w1it is designed

to give the learner the tools, the logic, and the thought proc­ esses that can be used in isolating a problem on the job. If it is an electrical problem, the information provided here ·will aid in determining the area of the defective component. This unit prepares you for the units that follo,v. Basic troubleshooting is discussed in Unit 26, advanced troubleshooting in Unit 27, and practical troubleshooting in Unit 28. The first part of this unit defines troubleshooting and discusses ho"v to narrO\V dovvn the problem quickly. Then ,ve discuss the steps needed to help find the specific problen1.

25.1 WHAT IS TROUBLESHOOTING? Any operating mechanical or electrical equipn1ent "vill at son1e time require service repair. Providing the diagnostic and repair work necessary to place the equip111ent back on line is one of the most important functions of the technician. The basic term that describes this type of \.Vork is troubleshooting. Troubleshooting is the process of detennining the cause of an equip1nent n1alfunction and performing correc­ tive measures to bring the equipn1ent back to normal operat­ ing parameters. Depending on the problem, this may require a high degree of knovvledge, experience, and skill. Basically, there are three types of problen1s: • Electrical problems ■ Mechanical problems ■ Co1nbined electrical/n1echanical problems. Whatever the nature of the problem, it is a good prac­ tice to follo,v a logical, structured, and systematic approach to solving it. By using a logical sequence when troubleshooting, the correct solution is usually found in the shortest possible time.

25.2 QUICK CHECKS FOR AIR CONDITIONING PROBLEMS Figuring things out: A seasoned technician will use a set of quick checks to detennine ,vhat is happening in an air con­ ditioning system. ()ne \\'ay to organize your troubleshooting thought process is to develop a plan of action. For exa1nple, use the word ACT as a ren1inder of ,vhat to check on an air conditioning system. It is in1portant to make these checks so that you do not end up on a v,ild-goose chase, embarrassing yourself and your co1npany. 489

490

UNIT 25

The abbreviation ACT is used to determine if the major components in a HVACR system are operating: A is for airflo,v. C is for compressor. T is for thermostat. Let us discuss how the ACT n1ethod is used as a quick ·way to check the vital signs of an air conditioning or refrig­ eration system. The order in which the vital signs are checked is not as in1portant as checking everything quickly before de­ veloping a diagnosis. For exainple, after you introduce your­ self to the customer, check the thermostat setting or the air filter if it is nearby.

A IS for Airflow Check the condensing unit airflo,�r. Is the airflo,v from the condenser warmer than the surrounding air? Hot air off the condenser means it is rejecting heat from the refrigerant. Check the indoor or evaporator airflo"'r· rs there airflow? Is the air from the supply grilles cold? Cold air means the evaporator and air distribution system are \-vorking. Figure 25-1 illustrates checking the temperature of the supply grille. Placing your hand at the grille ,vill not give you an accurate reading of the temperature or airflow·, but it ,-vill give you an initial indicator of ,-vhat is happening \Vith the supply air conditions. Note: Warm air being rejected by the condenser or cold air coming from the supply grille does not mean that the sys­ ten1 is charged properly. These checks are preliininary and used as a general indicator of what is functioning and "''hat is not functioning. Finally, if the condenser or indoor fan comes on, you knO'\-V that 24 volts is present in the control system and to the thermostat.

Figure 25-1 The troubleshooting process starts with a general

survey of the equipment. Determine if cold air when in the cooling mode or warm air in the heating mode is coming from the supply grille.

Figure 25-2 This manifold gauge set (shown not hooked up)

should have a pressure differential between the low-side and high-side gauges when the compressor is operating.

c Is for Compressor ls the compressor operating? What is the amperage dra\v of the con1pressor? Is there a pressure difference ben-veen the high side and lO\V side? Do not assume that the co1npressor is running. The condenser fan noise may override the com­ pressor operating sound. Checking the operating pressures and compressor amperage is an i1nportant part of this step. Figure 25-2 sho\.vs a manifold gauge set that can be used to determine if the compressor is operational. Because some condenser fa11s create noise that \Vill prevent the technicia11 from hearing the compressor operations, it is essential to in­ stall the gauges to detennine co1npressor operation. It is not advised to automatically install gauges on a sys­ te1n \\rith. less than 2 pounds of charge unless you are usi.ng lo,-v-loss fittings. Installation and ren1oval of the hoses cause loss of refrigeration, ,-vhich can significantly ilnpact a system with a small charge. rf you must add gauges to a system with a small charge, install the suction side hose only. There is less refrigerant loss on the lo,-v side ,vhen installing and removil1g hoses while the equipn1ent is running. Another ,vay to determine if the compressor is running is to check the amp dra,"' of the comn1on wire. Any wire on a three-phase con1pressor ,-vill do. For an initial check, this is a little quicker than hooking up the gauges.

HOW TO START ELECTRICAL TROUBLESHOOTING

■

491

";/

Figure 25-3 The thermostat should be checked to determine

if it is set to the correct mode, heat or cooling, and that the temperature is adjusted so that it is at least 10 degrees different than the room temperature. The thermometer temperature on the thermostat is not always accurate.

T Is for Thermostat ls the thermostat set to the cooling or refrigeration mode? Set the temperature 10°F below' the cooling setpoint to ensure that the unit will begin to operate and stay operating ·while troubleshooting. Ren1ember to reset the thermostat to the customer setting prior to leaving the job. Does the digital thern1ostat have a display? Some sys­ ten1s have a time delay. "\Vait at least 6 minutes before reach­ ing a conclusion. The indoor blo·wer 1nay be operating, but the condensing unit 1nay be on a ti1ne-delay circuit. Figure 25-3 shov.rs a blank screen. A blank t' stat screen indicates that there is no control voltage power. Search for the cause of the lack of control voltage, w-Ilich is usually 24 volts. In sun1mary, the ACT 1nethod or another logical method you devise ½rill eli1ninate parts of the syste1n that are ·working and help you diagnose the problem quickly. Each job is a lit­ tle different and developing a systematic ·way to start trouble­ shooting is important. Using the ACT 1nethod provides a fast and logical sequence for checking the system and, at the same time, familiarizes a technician ,-vith the system under scrutiny. Because n1ost malfunctioning problems are electrical, it is a comnJon practice to perfonn electrical troubleshooting first. If the problem is mechanical, the electrical analysis ½'ill usually point the technician in that direction. Because this unit is based on electrical troubleshooting, we will discuss the specific topic of electrical troubleshooting. Now· we take a look at quick checks for a heating system.

25.3 HEATING SYSTEM ACT TROUBLESHOOTING The ACT heating troubleshooting sequence is similar to the air conditioning troubleshooting sequence.

Figure 25-4 one of the ACT checks is to look for combustion

in a fossil fuel burning appliance. combustion is taking place in this three-burner gas furnace.

(C)

A IS for Airflow A is a reminder to check the airflo,v in the gas, heat pump, or oil furnace duct system. A is for airflo,v in handlers in electric heat, heat pumps, and hot ,vater coils. ls the air from the sup­ ply ducts ,vann, indicating that the heating system is ,vorking?

c Is for combustion C renlinds the technician to check for combustion of gas or oil heating systems. Can you see combustion? Figure 25-4 shows combustion in a gas furnace. Is heat coming fro1n the supply ducts? There is no co.mbustion in electrical heat, heat pu1nps, or hot ,vater coils, but the technician can check for supply duct heat. Hot ·water coils can be part of a gas, oil, or electric systen1; therefore, it would be logical to check the combustion operation of a gas or oil boiler. Check the amp draw· of an electric boiler.

T Is for Thermostat Is the thermostat set for the heating mode? Set the te1n­ perature l 0°F above the heating setpoint to ensure that the unit ,vill begin to operate. Does the digital thennostat have a display? Some syste1ns have a short tin1e delay, allo·wing the heat exchanger to heat prior to beginning indoor blo,ver operation. Re1nember to reset the thern1ostat setting to the customer setting prior to leaving the job.

25.4 USE YOUR SENSES The troubleshooting 111ethod just discussed relies on the senses of sight, hearing, feeling, or touch as sholvn in Figure 25-5: Seeing that the condenser fan is on. Seeing that the ther­ mostat is set correctly. Next, seeing that the pressures on the gauges are different, indicating that the compressor is creating a pressure difference. Finally, seeing the flames or combustion process in the case of oil or gas heat. The ACT method has the tech feeling for airflow out of the duct system.

492

UNIT 25

The sense of s1nell is also useful. Burned electrical com­ ponents or the scent of burned refrigerant ,vill lead the tech­ nician to explore electrical or refrigerant side problems. The least useful human sense is the sense of taste. It is not a practice to taste damaged HVACR components, refrig­ erants, or other chemicals used in our profession. Using the sense of taste can be dangerous to the technician. Do not use this sense for troubleshooting.

25.5 UNDERSTANDING BASIC TROUBLESHOOTING BY USING A VOLTAGE METER

Figure 25-5 The human senses of sight, hearing, touching, and

smelling are valuable troubleshooting tools. All of these senses are a valuable part of the first troubleshooting steps of gathering information.

Inspecting the syste1n is very important. Search for burned-out parts, components, or wires. Listen for the op­ eration of the system. Are the major systen1 components such as blo'A7ers or compressors operating continuously? Are they cycling on and off? Are unusual noises coming fron1 the co1npressor, blower, or heating system? The novice techni­ cian may not be able to pick up unusual noises, but ,,1,,'ith time and experience the sound of a correctly functioning system will be a valuable troubleshooting tool.

Technicians need to kJ10,v ho,v to select and use a voltmeter before trying to use this instrument for troubleshooting. Before technicians do any troubleshooting they need to kno\\' ,�1hat voltage reading to expect in varying circuit conditions. Let's look at the essentials to solving electrical proble1ns using a voltmeter.

Ways to Measure Voltage Voltage is measured across a voltage source. This n1ay be ob­ vious, but a circuit ,vithout voltage will not work. ()ne vvay to do this on an air conditioning system is to check the incom­ ing voltage to the major components such as the air handler or condensing unit. If the system is a spht system, as shown in Figure 25-6, it is helpful to determine if the problen1 is a high-voltage or lovv control voltage problem. Measure the voltage at the primary of the transforn1er. If the primary volt­ age is good, that means the air handler has the correct supply

COOLING -COIL FROM POWER SOUR FUSED DISCONNECT

..

CONDENS DRAI

RETUR1 -AIR DUCT

FURNACE �o· CO 'CRETE/ PAD CO DENSING UNIT

SPACE REQUIRED FROM U IT TO WALL CONTROL PA EL ACCESS WRAPPER

Figure 25-6 This is called

a split system. This means that the condenser section is separated from the evaporator section. The condensing unit is outside the building and the air handler and evaporator are inside the building. Notice the disconnect to remove power from the outdoor section.

HOW TO START ELECTRICAL TROUBLESHOOTING

493

230 VOLTS B. PRTh1ARY VOLTAGE CHECK

OFM

IFR

IFMC HEATING TDR

IFR

TRAN

COOL AUTO AT OFF

I I I I I

0 oFF 0

A. SECONDARY VOLTAGE

CHECK

PJLOT

PS 0

TB

ROONI THERMOSTAT

Figure 25-7 This diagram shows a quick way to determine if a system has an incoming voltage problem or control voltage problem. If the primary voltage on the transformer is good, check the voltage on the secondary side. Both of these voltages are required for the system to operate.

voltage. If the correct pri1nary voltage is present, verify the secondary side of the transfon11er as shovvn in Figure 25-7. Voltage ,,viii be measured across an open load. For ex­ an1ple, you do not k.no,v that the motor ,-vindings in a simple 1notor are open. Assu1ning that everything else is vvorking as designed, the technician will measure voltage across the mo­ tor even though it is open as illustrated in Figure 25-8. A me­ chanically locked-up blower motor \vill have supply voltage and good motor windings, yet ,-vill not rotate. Remove the pO\\'er fro1n the 1notor. Push-start the motor to see if it ·will turn freely. Seized n1otor bearings could prevent the motor from turning. The fan blade or blov,er wheel could be against

its housing, preventing 1notor operation. EC.lvis will not turn freely vvhen they are de-energized. The permanent magnets in the stator prevent the rotor from turning freely and evenly when de-energized. Voltage \Vill be measured across an open \Vire, open fuse, or open sv,ritch provided that voltage is present. The easi­ est ,-vay to understand this is by 1neasuring the voltage on a plugged-in po,ver cord. Be careful not to touch the \Vires to­ gether while the cord is plugged into the outlet. The voltme­ ter \vill display the \Vall outlet voltage on the plug prongs even though it may not operate an electrical device. Voltage •..vill be read across an open ,vire because the meter is measuring

494

UNIT 25

Figure 25-8 The compressor motor, �. may be defective even if the supply voltage is measured across it. Check the resistance of the motor windings. The motor could also be mechanically locked up.

Lz

CCHS

CCH C

CO!VIP

Il

PO\VER

CIRCUIT

!FR

HI 3

RC

7

HC I

LS

9

HEATER

FL

3 230V

potential difference. The voltage potential is available, but it cannot flo,-v since the ,vire path is broken or open. Figure 25-9 illustrates an open s,\ritch with the voltmeter 1neasuring the applied voltage across it. Voltage "vill be measured across an open fuse. An open fuse is like an open wire and is considered to have infinite resistance. It is best to re1nove the suspect fuse and check it ,,vith an ohmmeter. Figure 25-10 shows ho"'' to check the fuse \Vith an oh111meter disconnected from a circuit. The resist­ ance should be near On. Measuring resistance ivith applied voltage ·will damage an ohmmeter or at a minimum blo\v the meter fuse. Re1noving the fuse also prevents a resistance reading through another component that may be in parallel \Vith the fuse.

n

17 1_1 � l,

Where Voltage Will Not Be Measured \Toltage

will not be measured across a piece of \Vire or closed set of contacts v\rith the same potential. See the example in

FUSE NO RESISTANCE­ GOOD FUSE

Figure 25-10 Measure resistance across a fuse while it is removed from the system. This is a safety procedure and prevents the technician from measuring something else in the system.

I lOV

FAN :MOTOR

(l.vlOTOR NOT RUNNlNG)

Figure 25-9 The voltmeter will measure the applied voltage across an open wire and open switch.

Figure 25-11. The voltmeter is designed to measure a voltage difference, also kno\vn as a potential difference. Measuring voltage on one bare wire ,vith 240 volts flo,-ving through it w"ill not shovr a voltage reading since the voltmeter is measur­ ing the same voltage potential on the ,vire. Voltage will not be measured across a good fuse. The fuse is like a piece of ,vire and does not create resistance or a voltage drop; therefore, you ,vill get a zero voltage reading. Voltage \\/"ill not be measured across a closed (good) overload device. An overload device, like an external

HOW TO START ELECTRICAL TROUBLESHOOTING

11 l),-,1 Tf"" LI I '-''-' ::J

495

The person using this technique may or may not have an idea of hov.r the system is supposed to operate, so he simply starts to change out parts until the system begins to operate. One major disadvantage of this n1ethod is that there may not be anything vnong v.rith the circuit or its components. It may be a simple thermostat operating error or a switch that has not been turned on. Changing out a part that is obvi­ ously burned out is not considered a "parts changer" behav­ ior unless the technician does not try to find out why the component became defective. Some components burn out for a random and undeterminable reason, ,vhile other con1ponents ,vill quickly burn out again if the reason the compo­ nent ·was damaged in the first place is not found.

Individual Component Check Method

Figure 25-11 Voltage is operating the air conditioning system in this wire, but the meter measures o volts since there is no potential difference across the closed set of contacts. A good fuse with voltage running through it will read o volts. An open fuse will read the applied volts across it.

overload, is similar to a fuse. No resistance-therefore no voltage reading. Voltage will not be measured across a closed switch. A dosed S\Vitch has no resistance and ,vill have no voltage reading.

25.6 METHODS OF ELECTRICAL TROUBLESHOOTING There are n1any different methods of troubleshooting­ some good, some bad. Some work in one application, yet 1nay not ·work in another application. The follo,ving sections explore the 1nany ,-vays a technician can do troubleshooting. Read about these 111ethods and determine ·which method or methods ,vill ,vork for you. There is no one v,ray that is best, but there are some methods that are not acceptable. Read and decide for yourselfl

Guess and Check Method The guess and check 1nethod of troubleshooting is used by a person ,vbo has no idea of ho,v the equipment is supposed to operate. He starts by guessing and checking anything that comes to his 1nind. This method is most likely used by the person who has little or no experience or the experienced technician \Vho is asked to troubleshoot a system that is be­ yond her capabilities.

Part Changer Method The part changer 1nethod of troubleshooting is used by tech­ nicians who have a lov.' level of troubleshooting expertise.

The individual co1nponent check method is the second stage of the guess and check n1ethod of troubleshooting. The per­ son v.1ho uses the component check method relies on previous experience. The technician troubleshoots the components that he is most familiar ·with and overlook components that are unfamiliar. Again, luck is involved in finding the right de­ fective component(s)-not a good troubleshooting method.

SAFETY TIP Do not touch the metal part of the meter probes when measuring voltage or resistance. Touching the metal probe while measuring voltage may cause electrical shock. Touching both probes when measuring resist­ ance will read high resistance through the body. You will think the component has a complete circuit, yet a very high resistance.

Voltage to Ground Method Nlost circuits ,,vith properly supplied voltage ,vill measure voltage to ground even if a component is open. The voltage to ground n1ethod is good to use as a safety check to ensure that no voltage is present prior to touching a bare \Vire or an exposed co1nponent that 1nay be carrying voltage. In Figure 25-12, the upper condenser motor nun1ber 2 is not operating. It is not operating because the IR-I con­ tacts (circled in red) are burned open. As Figure 25-12 shows, voltage can be measured to ground \-vith an open component to the left and right side of condenser motor 2. Using this troubleshooting method, the technician may think that the condenser motor is defective since voltage to ground is meas­ ured on each side of the condenser motor. But changing the 1notor ,vould not solve the problem. Using the voltage to ground troubleshooting method leads to confusion and 1nisdiagnosis. It is a good safety step to ensure that no voltage is present prior to touching a com­ ponent. Do not think this is a valid troubleshooting method.

496

UNIT 25 08/ 30-3-60 SAI?l} 2 2 - 460-3-60

NO. I COMPRESSOR

IM 2 3

PO\VER SUPPLY - --0 208/230-3-60 480-3-60

4

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5

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3M

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lFU

EVAP. IvlOTOR TNHERENT PROTECTION

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9

NOTE:

10

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11 12

11TH

.--o--c-0-------.,_-�

IHTR

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1-----'

FOR 208/230-3-60 PO\VER SUPPLY, UNIT CONNECTED AS SHO\VN. FOR 460-3-60 POWER SUPPLY, \VIRES LI TO I AND L3 TO 3 ARE NOT USED. TRANSFORfvfER CONNECTED AS INDICATED BY ARROWS. COND. lvJOTOR NO. 2 INHERENT PROTECTION

13 14 CONTACT IS BURNT OPEN

1211 I

U

V

2 ---------.l---1'

15 16 17

7R

18

\HP

!LP

1-0L 2-0L

-----11-- - _I

19

2TH

20

3-0L

l

LO'vV A vJBIENT ACCESSORY

ITR

21 22 23 24

3T R

�---------2R

25 IR-2 26

---11------------- --------{

208 V TAP

27

230V TRANSFORMER 75 VA CONTROL CIRCurrs

Figure 25-12 Checking voltage to ground can lead to misdiagnosis of an electrical problem. In this example 1R-1 is open, but voltage is measured to ground on both sides of the motor, leading to confusing results. Measuring to ground is a safety measure, not a good troubleshooting practice.

HOW TO START ELECTRICAL TROUBLESHOOTING

the voltage is lost, the defective component, thermostat TC, is found. Is the thermostat open because the temperature is set too high or is the thermostat defective? Figure 25-14, which is part of a ladder diagran1, illus­ trates ho,v to use the hopscotch troubleshooting 1nethod. First determine the load and line side of the circuit, as shown in Figure 25-15. The load side is the side of the circuit that has the co1nponent ,vith the greatest resistance. The line side ,vill have svvitches and safety devices. Connect one voltmeter probe to the right side or load side of the circuit to start the hopscotch troubleshooting procedure. The process is simple. We n1easure voltage across all closed s,vitch contacts until ,,ve cross over the load. Once the probe crosses over to the right of the load, the voltage being measured is the same, therefore the meter ,-vill have a zero-volt reading. The voltmeter only measures potential difference and having the voltmeter probes on the same side of the po,ver supply ,vill measure zero volts even though serious voltage is present. Figure 25-16 sho,vs an example of ho,v to use the hop­ scotch method to troubleshoot an open compressor thern10stat ( CTHI). Attach one meter probe to the right side or load side of the ladder diagram. This can be done by securing a meter probe "vith an alligator clip. Start by measuring the supply voltage to the circuit ,-vith the other probe. The sup­ plied voltage should be measured across each component until you reach the defective component. In this case, 230 volts ,vill be measured all the ,vay to the left side of the open thermostat, as sho\.vn in Figures 25-17A, 25-l 7B, and 25-l 7C. Here is the hopscotch sequence of events:

SAFETY TIP

I

Prior to using your voltmeter for voltage reading, test it against a known source of voltage such as a wall outlet or other voltage source. A defective voltmeter or open meter probe will measure zero volts and give a false and unsafe non-reading.

Hopscotch Troubleshooting Method The hopscotch troubleshooting method is a recomn1ended vvay to find a defective component or open \.Vire. The hop­ scotch method involves measuring voltage by jumping through a circuit until the voltage is lost. Detern1ine the load side of the circuit and hopscotch the control system to find the fault. The load side of the electrical circuit is defined as the side of the potential closest to the majority of the povver­ constuJ1ing devices. The hopscotch method requires the use of a ladder wir­ ing diagram as ,ve previously sa,v in Figure 25-8. First, ,ve examine ,vhat circuit voltage is expected ·when jumping or hopscotching through a circuit. Figure 25-13 sho,,vs an ex­ a1nple of the hopscotch method of troubleshooting. When

VO:tvl

0

Ll

L2

230 volts i.s measured on the right side of CRl. ■ 230 volts is measured on the left and right side of LPL ■ 230 volts is measured on the left and right side of HP. ■ 230 volts is measured on the left and right sides of both 011 and OLI. ■ 230 volts is measured on the left side of CTHL ■

230 230 230 VOLTS- - - ... VOLTS - - .. - .. VOLTS ---·-----� 0VOLTS ,,

-

Ivleasurements on the right side of the open thermostat "vill be zero volts, as illustrated in Figure 25-18. Verify that the thermostat is truly defective. An open CTHI, sho,vn in Figure 25-19, \.VilJ have the supplied voltage measured across it. Once it has been established that the thermostat is open, the technician needs to check that the thennostat is defective by ren1oving it from the circuit. Using an ohmmeter to check the thernlostat, the thennostat ,vill be infinity or open, as sho,vn in Figure 25-20. If it is an open thermostat, allo,�, the device, in this case a

I

LOAD

Figure 25-13 This is an example of a simple hopscotch

method of troubleshooting. As shown in this diagram, the voltage will be lost when a switch or safety is open. The voltage will also be o volts when it jumps to the right side of the open thermostat TC.

Ll

1-----------------

CRl

LP 1

HP 1

230 VOLTS OL I

L2 ----------------i

OL 1 1------14

Figure 25-14 Circuit extracted from a ladder diagram.

497

498

UNIT 25 L2 LI i-+---------------- 230VOLTS---------------CR I

LPI

HPI

OL 1

OL l

CTH I

>--N-< 6 >---0-,-0-----Ve discuss problen1s using diagrams, vve will trou­ bleshoot some of the major component parts of an air con­ ditioning system, such as a compressor. Many parts of this book have troubleshooting tips built into the units. This sec­ tion will refresh and expand on those troubleshooting tech­ niques. For example, the hopscotch troubleshooting 1nethod ·was discussed in detail in earlier units. lt ,viii be used to solve some of the diagram problems presented. Learning ho,-v to troubleshoot is the most important skill you \.vill need as a service technician. Lesser skilled techs can 542

change out a contactor or compressor. But deterrnining that those cornponents are defective takes more knowledge, skill, and experience. Troubleshooting skills co1ne with practice and listening. Listen and learn from other techs who have found solutions to HVACR problems. It seems that one com1non trait of HVACR techs is their ,.villingness to share a success story. You can learn fron1 others' experiences \vithout being on the job; of course, the best learning tool is figuri.t1g out the problem yourself. As stated earlier, there is not one right ,vay to troubleshoot as long as you come up vvith the correct answer in a reasonable a1nount of time. Use your "lifelmes" ,-vhen you need help. Do not call for advice in front of your customer. Sometimes it is a good idea to step a\vay from the problem for a short \vhile. Go on a short break or get gas for your vehicle. Stepping away may clear the clouds that we all get from tune to time in the troubleshooting process. You '\>vill be presented "'rith some proble1ns here. Step back and evaluate the infonna­ tion. In the problems presented in this unit, determine what you thi.tlk is \Vrong before reading the solution.

SERVICE CALL 1: HOPSCOTCH PRACTICE This service call problen1 is used to review your skills using the hopscotch troubleshooting n1ethod and give you an ad­ ditional tool for troubleshooting intermittent problems. The first service call of the day involves an air condition­ ing unit that occasionally cycles its pressure s,.vitch off and on, known as short cycling. This seems to be the only prob­ lem. For this example the problem has been isolated to the energized circuit sho'\>vn m Figure 28-1. It is a simple high­ voltage control circuit with CR contacts and lo\v-pressure and high-pressure switches in series with©, the compressor contactor coil. CR, LP, and HP \Vill be closed \Vhen the cir­ cuit is energized and there is adequate refrigerant pressure in the system. \-\That should the voltage reading be across each co1npo­ nent? Determine your answer before proceeding. Using the hopscotch method of troubleshooting, you should measure 120 volts up to the contactor \Vindi.ngs. The po\ver supply is represented by Ll and N. The Ll and N power supply is 120 volts. vVhen you see the terms Ll and L2 on a diagrarn, it would most likely be a 208/240-V po,ver supply. When using the hopscotch troubleshootmg method, a loss of voltage n1eans that one of the S'\>vitches is open. Figure 28-2 shows the voltage reading "''hen the system is operating properly.

PRACTICAL TROUBLESHOOTING Lt

CR

3

543

N

LP

HP

C

Figure 28-1 The problem for service Call 1 has been isolated to the circuit shown here. This circuit has control relay contacts CR 1 and 3, low-pressure switch LP, high-pressure switch HP, and compressor contactor coil@. LL

CD

CR 3

l20V

N

LP

HP

C

(!)

Figure 28-2 Hopscotch sequence: When the circuit is operating properly, attach one voltmeter probe to the right side of the circuit. With the second voltmeter probe, start measuring voltage on the left side of CR. The voltage will drop to o volts when it crosses the motor contactor@.

Step 3: Supply voltage is Lneasured on each side of the switch devices such as CR, LP, and HP, (points 2, 3, 4, 5, and 6).

Referring to Figure 28-2, folloV\7 the hopscotch sequence ,vhen the circuit is operating normally: Step I: \A/hen the circuit is operating properly, attach one vol.tn1eter probe to the right side of the circuit, point 7. Step 2: With the second voltmeter probe, start meas­ uring voltage on the .left side of CR (point 1).

Step 4: The voltage \vill drop to O volts v-rhen it crosses the motor contactor coil(Qat point 7.

TROUBLESHOOTING 28.1: HOPSCOTCHING A SHORT CYCLING SYSTEM In going back to the short cycling problem, let's now inves­ tigate how to find the solution:

O Figure 28-3 illustrates the reason why the compressor

e

contactor is not energized continuously.

The low-pressure switch is open, across points 2 and 3, therefore no voltage can travel to the left side of the contactor coil©.

E) Using hopscotch troubleshooting, you notice that the

120-V supply voltage is lost once the meter probe jumps to the right side of the low-pressure switch at point 3. The right side of the low pressure switch reads o volts, at point 3.

O Since the LPS is open, o volts will be measured at

e

remaining points 4 and 5. There is no need to make any more measurements when o volts is found to the right of an open component.

In Figure 28-4, you verify a 120-volt reading across the low-pressure switch at points 2 and 3. This voltage measurement indicates that the LPS is open. Is the switch open because it is defective or because the system pressure is low? The remaining steps will help you solve the specific problem. Before we can isolate the problem hook up the manifold gauge set to determine if the system is low on charge.

(continued)

544

UNIT 28 120V

Ll

1

CR 3

• LP

120V

ov

0

•

N

HP

C

0

Figure 28-3 The hopscotch method of troubleshooting measures voltage starting at the left side of the diagram and measuring voltage as it jumps to the right side of the diagram. When voltage is lost, as is the case with the open low-pressure switch, the voltage on the right side of the pressure switch drops to zero volts. Ll

I

CR 3

120V

N

LP

HP

C

Figure 28-4 After determining that the problem is an open low-pressure switch, it is important to verify that this is really the problem. N

Ll

CR 3

LP

HP

C

JUMPER

Figure 28-5 Jumper placed across an open low-pressure switch to verify it is defective.

If the suction pressure is high enough, then the low­ pressure switch is defective.

O To verify a defective low-pressure switch, first turn off

the power. Then use a set of alligator clips or jumper wire to short across the defective switch as illustrated in Figure 28-5.

0 Turn the power back on.

The system should operate, unless there is another problem. Watch the low-pressure gauge when the condenser starts to ensure that the suction pressure does not drop below it normal operating pressure. The jumper should only be used as a temporary fix until you can get a replacement part. Too many times this temporary fix becomes permanent.

PRACTICAL TROUBLESHOOTING

TECH TIP

FUSE HOLDER

This Tech Tip relates to the Troubleshooting 28.1 exercise. Once it has been determined that the problem is an open low-pressure switch, it is important to verify that this is the problem. Voltage will be measured across an open switch when voltage is applied to both sides of the circuit. This verifies that the low-pressure switch is open. It can also be verified by turning off the power to the circuit. Disconnect the low-pressure switch leads and check the switch with an ohmmeter. An open switch will measure infinity. If the switch is good and the pressure increases, the low-pressure switch will reset and the resistance will be near o Q.

Finally, so1ne problems are difficult to solve unless the event occurs ,vhen the technician is at the job site. For exan1ple, the lo,�7or high-pressure switch 1nay open due to random conditions that may occur periodically but do not occur vvhen the technician is on the job. A good procedure for finding the culprit follo\vs. One "'ray to determine if a safety device opens during op­ eration is illustrated in Figure 28-6. Use a 1/ 10-amp fuse or smaller across any safety device that may open and reset when the adverse condition is created. When that safety con1ponent opens, the power ,vill be directed through the fuse for a short time period until it blo,.vs. That is v\7hy a low-amperage fuse is used: It ,vill blo,.v because the current flo"¼1 is higher than its rating. When the technician returns to the job, the blo,.vn fuse \vill be an indicator of the problem. It ,vill not solve the problem, but it will narrow it dovvn to the device that has the open fuse. The technician can then focus on the proble1ns that ,vould make that specific safety device open.

TECH TIP Have a fuse holder and spare fuses available for trou­ bleshooting. A fuse holder is shown in Figure 28-7. Use a glass fuse holder or automotive fuse holder. You will need very low amperage fuses to install across opening safeties and a 5-amp in line fuse to protect the secondary side of a 24-V, 40-VA control transformer. These are all installed on a temporary basis. The 5-amp transformer fuse is a good idea because a short circuit or a high load condition may have caused the transformer to open. Ll

CR 3

545

FUSE

I •

CUT \VIRE AND INSTALL F.I\Cll END ACROSS THE PRFSSl'.RE S\VITCH

Figure 28-7 Techs should have a fuse and fuse holder with connection wires available for troubleshooting. The red wire is cut, insulation stripped, and then placed in series with the circuit it is to protect.

Time on the job: Initial time on this job is 1 hour looking for a problem that does not occur w-hen the tech is there. Many times the problem is not solved .if it is intermittent. There ,-vill be a return ticket to solve the problem if it occurs again. Total time on the job is undeternrined at this tune. It \vill depend on how quickly the intermittent problem occurs and can be identified.

SERVICE CALL 2: INADEQUATE HEATING You are on a ,vinter service call. The customer coinplaint is a lack of heating, especially at night. Use Figure 28-8 to determine the solution to this problem. Enlarged Electrical Diagram ED-1, found in the Electrical Diagrams package that accompanies this text, 1nay also be used in this exercise. Here is the troubleshooting sequence of events: ■ You arrive on the job and the heating system is ½ 0rking. • \Varm air is felt coining fron1 the supply grille. ■ Ne>.1:, you check the amp draw of the heat strip. The heat strip is dra,ving about 20 amps, which is sho"¼1n by the 7

N

LP

HP

C

e------:-i l i-:::,________.-,-0...,---,-o-,-i:>-r------�rvv"""}------6

FUSES Figure 28-6 One way to determine which safety device opens during operation is to temporarily install a 1/10-amp fuse across any safety switch.

546

UNIT 28 L2

Figure 28-8 This is a ladder diagram for a heating and cooling package unit. The heating source is electric. The dashed rectangular box is the thermostat. Diagrams are not drawn to scale as indicated by the large size of the thermostat.

CR

LP

HP

IFR lFl\-1

2

HR

EH

20A

CR

HL OFJvl

4

CR

CH

5

4

240V 24V HR

�--------------------------,

I I I I I

ON

6

G

4 5

AUTO R

• I I I I I

e I

y

COOL

HR CR

OFF

w

HEAT

TH

IFR

I

HR

'--------------------------�

I

red circle on the diagram. This is in the nonnal range for a single-phase heat strip operating at 240 volts. ■ After the electric furnace has been operating for about 1 5 minutes, the amp drav., drops to zero. ■ You check the thermometer on the thermostat and it is several degrees cooler than the temperature setting, therefore the heating system should still be operating. ■ The blo,ver is moving air, but it is getting cooler. You begin to generate reasons ,-vhy the heat strip is cut­ ting out. What are the possibilities? Look at the diagram and see what you think. \\That are some reasons the heating sys­ tem is cutting out? From previous experiences the most likely problem is the high limit, HL, is opening. It 1nay be opening at a lo\\'er than normal te1n.perature or possibly low airflow is causing the heat strip to overheat and open the high limit. Lo,v airflo,v or short cycling could be caused by: 1

✓ A dirty filter

I

✓ A dirty evaporator ✓ Other duct restrictions ✓ The blo,-ver speed could be set too low or the blov.rer could be slo,ving do,-vn after it ,-varms up. Sometitnes bearing ,vear causes the bearings to drag and slo,v do,-vn the 1notor. Eventually the drag ,vill overheat the motor and the 1notor ,vill cut out on its internal overload. ✓ Another problem could be the thennostat opening pre­ maturely and stopping the heating process. To find the exact problem you should use the hopscotch troubleshooting method to detennine ,vhich component is opening in the electric heat EH line in Figure 28-8. Voltage ,vill be lost across the open component. Doing hopscotch troubleshooting you determine that the high litnit, HL, is opening. Here are the voltage readings: ■ The left side of HL has 240 volts. ■ The right side has O volts; 240 volts is measured across the open HL.

PRACTICAL TROUBLESHOOTING ■ Now you need to determine if the high limit is defective or if it is an airflow problem. ■ The temperature rise across an electric strip heat is about 50° to 60°F. In other words, if the return air is 70°F, then the supply air should be in the range of 120 ° to 130°F. Higher supply air temperatures indicate that the airflow n1ay be lo,\1'. You measure 145 °F from the supply grille nearest the electric furnace. This is an indication of a lack of airflow. What are some conditions that \\Till cause low airflo,v? Here are some steps to take ,vhen investigating lo\.v airfl.o,v conditions: 1. Check the air filter. Inspection reveals that it is fairly clean. 2. Inspect the evaporator. Inspection reveals a mat of dirt. 3. After cleaning the evaporator, you inspect for other airflo,v restrictions. 4. The blo·wer \\!'heel is caked \\l'ith dirt. The blower ,-vheel i.s re1noved from the motor shaft and taken outside and cleaned. No other duct restrictions are noticed. After doing this service, 1neasure the rise in ten1perature again. The supply air temperature has dropped from 145° to 120°F. Verify that this solved the problem by watching the furnace operate until it has satisfied the thermostat setting of 70 °F. The amperage on the heat strip ,-vas n1easured \vhile in operation. The heat strip did not cut out. The service \\Tork you perfonned will also help the per­ formance of the cooling systen1 next spring. You recom1nend an annual clean and check progran1 so that this ,-vill not happen again. Time on the job: Total time on the job was 2 hours. Most of the time involved cleaning and n1aintenance of the system. This is routine maintenance and is something you should en­ courage the custom.er to schedule \vith your company.

'

TECH TIP When changing out a transformer that controls cooling and uses gas heat, be sure to check the polarity of the secondary of the transformer. The secondary has a hot side and common side. For example, let's say another tech changed a defective transformer during the cooling season. When the heating season arrived, the gas furnace acted erratically. Sometimes it would heat and other times it would not. The circuit board was blamed. The thermostat was blamed. Bad connections were blamed. It turns out that the tech did not observe the transformer polarity when changing it in the summer. Switching the position of the two secondary wires did the trick.

SERVICE CALL 3: "NO COOLING" CALL FOR A 5-TON PACKAGE UNIT This service call sends you to a small office space \\Tith a 5-ton package unit, as shown in Figure 28-8. The system is silent, nothing is operating. The "silent treatment" is usually the

547

easiest type of proble1n to solve. After meeting ,vi.th the build­ ing manager, you notice that the thermostat is set for cooling and the thermostat setting is 10° F belO\\T the room tempera­ ture of 85°F. You place the thermostat in the Fan On 1node and the blo,ver begins to operate. What does this tell you? This should tell you that there is supply voltage and that the secondary of the transforn1er also has 24 volts. Without 24 V on the secondary side of the transformer, the@coil in the control circuit \.vould not energize the IFR contacts to operate the indoor fan motor @B). This simple check \.\Till sho"" you that both supply and control voltage are present in the package unit. Here is the sequence for solving this problem: 1. Using the diagran1 in Figure 28-8, you hopscotch the thermostat circuit by attaching one voltmeter probe to the right side of the 24-V transformer. 2. Next you measure 24 volts on the Rconnection. The Rcon­ nection ,..,,jll be on the t'stat or the red ,-vire feeding the t'stat. 3. Voltage is lost \.vhen jumping over the thennostat to the Y connection. This indicates that the thermostat is open. 4. Measuring across Rand Y, you find 24 volts, again veri­ fying that the t' stat is open. 5. Before replacing the thermostat you want to be abso­ lutely sure that the problem is the thern1ostat. You place a jumper ,-vire across the R and Y terminals and the system begins to operate normally. You report the problem to the building manager who approves the repair. You notify the manager that you \\Till leave the ju1nper connected until returning from the supply house \\Tith a replacement thermostat in 30 n1i11utes. This will start the cooling process ,.vhile you are gone. On your return, the replacement is installed and system operation verified. \IVhile ,�1aiting for the system to cycle, you confirn1 that the refrigerant charge is correct. It ,-vould be an embarrass1nent if the syste1n \.Vere low on charge, requir­ ing an additional service call scheduled for this overlooked proble1n. A complete system survey is important. Your doc­ tor does a complete check-up even if you only have a sore throat. The HVACR "doctor" should do the same.

TECH TIP When going on service calls, always check in with the owner, building manager, or person requesting the serv­ ice. Ask them to explain the problem and show you where the equipment is located, including both inside and out­ side units. Ask for a brief history of the problem and re­ view any service tickets from work previously completed on the equipment. This will ensure that you are working on the correct system, plus you will have a better under­ standing of the problem. The service calls discussed in this unit recommend that you complete these steps prior to beginning the troubleshooting process. This is part of what we like to call "customer service." Discuss the cost and outcome of your troubleshooting before doing any work and also when completing the work.

548

UNIT 28

SERVICE CALL 4: INADEQUATE COOLING

setting is okay. The airflow is good. The filter is clean. The condenser coil looks clean. It seems to be an electrical prob­ ]en1. Troubleshooting 28.2 follow·s the steps that \vill help you determine what is happening.

Your last call of the day involves inadequate cooling at a residence. The compressor is short cycling ( cutting on and off) about every 3 to 4 minutes. You find that the thermostat

TROUBLESHOOTING 28.2: SHORT CYCLING COMPRESSOR

O If the system is energized, CR will be closed between points 1 and 2. O 240 volts is measured on the left of the high-pressure

Use Figure 28-9 or enlarged Electrical Diagram ED-8, found in the Electrical Diagrams package that accompanies this text, for this exercise. Using the hopscotch procedure, you measure the following voltages:

switch HPS (point 3).

O 240 volts is measured on the left and right sides of the CR contacts (point 1).

Ll

LEGEND

L2

•---------240/1/60 ---------

COMP C

C RC CFM

COMP: C: lFR: IFM: CR: HPS: LPS: CR: CH: TRANS: ClT: CT: RC:

lFM IFR

08 CR

•••••• HPS

LPS

CH

CR

R

Figure 28-9 The ladder diagram is used for hopscotch troubleshooting. The VOM is hooked up for the troubleshooting procedure. This is a simplified cooling diagram without heat.

AUTO y

THERMOSTAT

CR

COMPRESSOR CONTACTOR lNDOOR FAN RELAY INDOOR FAN t.10TOR CONTROL RELAY HIGH-PRESSURE SWITCH LO\V-PRESSURE SWlTCH CONTROL RELAY CRANKCASE HEATER TRANSFORMER COMPRESSOR lNTERNAL THERtv10STAT COOL THERMOSTAT RUN CAPACITOR

PRACTICAL TROUBLESHOOTING

O 240 volts is measured on the right side of the high­ pressure switch HPS (point 4). 8 240 volts is measured on the left side of the low­ pressure switch LPS (point 5).

(;) o volts is found on the right side of the low-pressure

549

O o volts is found on the left side of the compressor inter­ nal thermostat CIT (point 7). O o volts is found on the right side of the compressor internal thermostat CIT (point 8).

switch LPS (point 6).

What is the ans,,ver to this problem? One important troubleshooting tool left out in this exercise is the pressure readings on the manifold gauge set. This is an open lo\v-pressure switch (LPS) problem. Is the pressure S\Vitch open because of low pressure or is the lo\v-pressure switch de­ fective, opening at a higher than normal pressure setting? Was the low·-pressure s·witch recently changed? If so, ,,vas the correct one installed? For instance, the low-pressure s·witch cut-out for systems using R-410A is much higher than the lo\·V-pressure S'vvitch for R-22 systems. The R-410A lovv-pressure S\Vitch ,vill get to opening pressures quicker if installed on a R-22 system. Another consideration is the state of the evaporator coil and air filter-are they clean? The coil may appear clean but it should be flushed anyway. Dirt could be embedded between the coil fins. Before replacing the low-pressure s·witch, confirm that the svvitch is the problen1. Jumper the svvitch and check the lo,v-side pressures. The system may be lo,v on charge and/or have low airflow. After the lo\v-pressure s,'1-ritch is replaced, create a lo\v-pressure condition and test the operation of the pressure s,vitch. This \vill check the operation of the switch and your ,,riring job. You can also test the operation pressure of the S\Vitch using nitrogen pressure hooked to the manifold gauge set and po,ver svvitch.

SAFETY TIP Many high-pressure switches do not have a Schrader valve fitting under the screw-on high-pressure connec­ tion point. Refrigerant must be recovered prior to remov­ ing the high-pressure connection or you will lose the refrigerant.

SERVICE CALL 5: LACK OF COOLING Refer to the package unit shown in Figure 28-10 (or enlarged Electrical Diagram ED-5 packaged '"'rith this text) as you try to solve this cooling problem. After a quick IO-minute survey of the job, you determine that the co1npressor is short cycling about every 4 or 5 minutes. The indoor blower section and condenser fan are \.Vorking properly. You take control of the system at the unit disconnect by shutting the system dovvn and installing the gauges and clan1p-on ammeter on the compressor com1non lead of the single-phase compressor.

Once the test instrun1ents have been connected, you close the disconnect, \.vhich \vill supply po,ver to the package unit. The system has a time-delay circuit controlled by TM, therefore the syste1n will not come on for about 5 minutes. Once the system comes on, the pressures stabilize to their normal readings. The clan1p-on am1neter, vvhich is con­ nected to the co1nmon on the con1pressor, is running a cou­ ple of ainps higher than RLA. After the syste1n operates for about 10 minutes, the compressor shuts down. You wait for the timing circuit to finish, and the compressor comes back on again ,vi.th normal pressures ai1d the higher than normal compressor amperage. During this cycle the compressor cuts out a little quicker. What is causing this problem? The focus seems to be the high amperage dravv. What safety device is causing the co1npressor to shut do,-vn? Reviewing the diagram you notice that the compressor has two overload devices labeled 011 and 012. 011 is used to protect the compressor by monitoring an1perage dra\v through the common terminal. 012 protects the start wind­ ing fron1 a high-current condition. (Note: The OL 1 and OLz thern1al sensors located in the high-voltage area around the compressor have contacts located in the high-voltage control section near the timer n1otor TM.) The normally closed contacts associated with 011 and 012 are found in the high-voltage circuit between the high-pressure switch (HPS) and the timer circuit connection B2. You want to be certain that the 011 contacts are opening before continuing the diagnosis. The HPS and 01'2 are also in that line. It is not likely that either of these con1ponents is the problem since the system head pressure is not high and the start ""rinding is es­ sentially out of the circuit a second after the motor starts. You should confirn1 this, however, before continuing. To verify the problem, you set up your DMM to hop­ scotch the circuit. Use Figure 28-11 to focus in on this part of the troubleshooting sequence. One probe is attached to the right side of the diagram, Lz. With the unit operating and preparing to use the hopscotch troubleshooting method, you record the follo\ving voltages: • 230 volts on the left side of C ■ 230 volts on the right side of C ■ 230 volts on the left side of contact 011 ■ 230 volts on the right side of contact 01 1 ■ 230 volts on the left side of contact OL 2 ■ 230 volts on the right side of contact 012•

550

UNIT 28 Lz

--- - - - - --230-1-60--- - - - - ------i� SR

SC

C

C

cc

CH COivlP CR Fivf FS GV HPS HR HS IFM LPS LS OL PS RC SC SR T,

RC

COMPR

CONDENSING UNIT

HR

HR

BPS

B

CR

Tz

T:i T4 T\\,1

FM

CH

CR

AHA C CAP

\VSV

COOL i

cc

COOL

OFF i----,.,_o,.--

HEAT

THER.1'-10STAT

CONT

OFF A.HA

24V

T,

24V

LEGEND ADJUSTABLE HEAT ANTICIPATOR COJ\.1PRESSOR CON TAC TOR S TARTING CAPACITOR COOLING C0\\1PENSATOR CRANKCASE HEATER COMPRESSOR CONTROL RELAY CONDENSER FAN IvIOTOR FAN S\VITCH GAS VALVE HIGH PRESSURES TAT HOLDING RELAY HUMIDISTAT INDOOR FAN MOTOR RELAY LO\V PRESSURESTAT LIMIT S\VITCH OVERLOAD PlLOT SAFETY RUN CAPACITOR START CAPACITOR S TART RELAY CONDENSING UNIT TRANSFORMER FURNACE TRANSFORMER HUMlDTFlER TRANSFORMER FILTER TRANSFORl'vlER TIMER \\10TOR WATER SOLENOID VALVE

AUTO

�

HEAT

LS

T2

IFR lFR

FURNACE

T4

ELECTRONIC FILTER U

24V

HUtvHDlFIER

HS

,__________ 115 VAc FURNACE--------P O\\'ER

Figure 28-10 This is a diagram of a gas cooling and standard air conditioning system. The legend and ladder diagram format make it a valuable tool for troubleshooting.

PRACTICAL TROUBLESHOOTING

-

- ------ -230-1-60-- - - - - - - - -

SR

SC

C

This diagram is an excerpt from Figure 28-10 used for Service Call 5. Figure 28-11

C

C0lv1PR

RC

After 10 1ninutes of operation, the compressor shuts do·wn. You notice the clamp-on an1meter dropping to zero and that the high- and lovv-side pressures on the mani­ fold gauge set have begun to equalize. You go back to the hopscotch measurements again and record the follo,ving readings: ■ ■ ■ • ■ •

551

230 volts on the left side of C 230 volts on the right side of C 230 volts on the left side of contact OL 1 0 volts on the right side of contact OL1 0 volts on the left side of contact OL2 0 volts on the right side of contact OL2.

Once you read O volts on the right side of Olp you can stop the hopscotch troubleshooting process and 1neasure di­ rectly across the 011. The supply voltage, 230 volts, ,-vill be measured directly across the open safety. This safety device is a thermal or ten1perature-sensitive device, therefore when it cools it ,.vill close the contacts and reset to its normally closed state. After feeling assured that the problem is that a high­ an1perage condition is causing 011 to open, you must decide hat the reasons are for the high a1nperage dra,,v. \,Vhat do you think? Here is a list of possible problen1s: 1

\\

l. Low operating voltage. This could be caused by the en­ ergy provider. Also, carbonized contactor points create resistance and lovver voltage supply to the compressor. Check the voltage on the output of the contactor when the cotnpressor is operating. Check the voltage drop across the closed contacts with operation. The voltage drop across the closed contacts should be zero volts, but no more than 3 volts. 2. Tight conipressor motor bearings. These vvill cause high­ amperage operation because the motor is turning under a lot of resistance. This problem is not possible to verify without a compressor teardovvn and autopsy. 3. Defective run capacitor. An open or ,-veak run capac­ itor "'ill cause the n1otor to dra,,v more amperage. Check the capacitor microfarad rating with a capaci­ tor checker. If it is off by more than ±lO 120 V is present. The red arro\.v points to this section. ■ Right side (point�) of COMPl, 120 V. • Both sides (points[:2] and [DJ) of CWFS, 120 V.

■

Use Figure 28-15 > an excerpt from Figure 28-13, to con­ tinue tracing the follo\.ving points in the troubleshooting process: • Both sides (points[I]andln]) ofF/Sl, 120 V. ■ Both sides (points[nJand II2]) ofT/S1 > 120 V. • Both sides (points� and [ZI) of LPSI and (points 17 and 19) HPSl, 120 V. ■ Both sides (points [21and!TI]) of TMRl, 120 V. Use Figure 28-16, excerpted from Figure 28-13, to con­ tinue tracing the follo,-ving points: ■ ■ ■ ■

Both sides (points[Ill and�) of Cl-NO, 120 V. 120 V at L (point�) of OFSI. 0 V at M (point In!). Both sides (points�andrn) ofCl-OL, 0 V.

Based on this information > ,-vhat is the problem? The contacts behveen Land M are open (points !251 and In!). This is the contact for the oil pressure s·witch #1. The oil pressure safety switch vvorks on a pressure differential behveen the suction pressure and oil pump pressure. The oil safety S\.Vitch has a start-up time delay of 2 to 3 minutes. When the co1npressor starts the suction pressure and oil pump pressure are nearly equal. The time delay allow·s the

llU,L OF MATERlAL MARK Cl-1 Cl-201. CBl-2 CB3

QTY.

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§

@) MARKEDTER.Ml'IAL

0 UNMARKED TERMINAi.

Ovatt-hour

GFCI GND

LED LOTO LPS LRA

MCA MOP MOV

NC NEC NEMA NFPA NO OL

PF PPE PSC PTC

R RMS RPM RVS

TD

16

UL

l

20 1

,.. :>

2

,.. :>

20 3

Light-emitting diode Lockout/tagout Lo,V'-pressure svvitch Locked rotor amps

6

Maximum circuit ampacity l'v1axirnum overcurrent protection Metal oxide varistor

7 19

Norn1ally closed contacts National Electrical Code National Electrical Manufacturers Association National Fire Protection Association Normally open contacts

l

21 6 14 3 17

Overload Po,-ver factor Personal protective equipment Permanent split capacitor motor Positive thermal coefficient

5 3 14 15

Resistance Root n1ean square Revolutions per minute Reversing valve solenoid

1 3 14 24

SAEJ429 Society of Auton1otive Engineers;

SEER

Unit

standard for mechanical and material requirements for externally threaded fasteners Seasonal energy efficiency ratio

4 7

Temperature difference (between the return air and supply air)

21

Undenvriters Laboratories

4 567

568

APPENDIX A

Term

Definition

Unit

Tern1

Definition

Unit

V

Volts Volt-amps

1 8

y

Letter designation for the cooling terminal on a thennostat

11

Watts Letter-number designation for the second stage of heating on the thern1ostat

1

Greek S)'lnbol for resistance or oh1ns

1

VA

w

W2

l1

APPENDIX B

HVACR Formulas BASIC FORMULAS Btu's = 500 X GPM X I watt = 3.413 Btu

�T

I kW= 3,413 Btu

I ton

=

OHM'S LAW AND WATT'S LAW WHEEL Use the Ohn1's law and Watt's law ,-vheel to help determine values of amps (I), volts (E), ohms (R), or watts (W).

12,000 Btu

Motor kW= V X AX 1.73 X PF+ 1000 Motor tons

= k\iV X

$

3,413 + 12,000

!Wms

■

amps X ohms (V = IX R) Watts = volts X amps (P = V X I)

■ Po,-ver factor ■

=

= R1

■ T·wo resistors in parallel

w

X

Al\1PS

?

Al\1PS

E

OHMS

R

VOLTS AMPS

X

X

OHMS

= --­

l

' £...

AMPS2

+ R2 R 1 X R2 R1 + R2

■ Multiple resistors in parallel

1 Rr

I

VOLTS

,vat.ts vo1ts x amps

Resistance in series

\VATIS AMPS

VOLTS OHl\1S

=

�

OHNIS

WATTS VOLTS

KEY FORMULAS ■ Volts

w�x

-VOHMS

VOLTS2 OHMS

=

- ---------

R i + R2 + R3 + ... ■ Capacitance in parallel = C 1 + C2 C1 X C2 ■ Capacitance in series = C1

+

current-Amps volts I=-oh1ns

C2

watts volts

watts --=I ohms

Pressure-Volts E=

watts = amps x ohms = E Vwatts X ohms = -a1nps

Resistance-Ohms volts R=-amps

volts2 ,vatts

,vat.ts --=R amps2

Power-watts V\T

= volts X

amps

= amps

2

X ohms

=

volts2 -ohms

=W

569

570

APPENDIX B

THREE-PHASE VOLTAGE Horsepo\ver

=

L1 I L1 ------------�

1. 73 X amps X volts X n1otor efficiency 746

230 or 480V

X po"''er factor (Actual)

SINGLE-PHASE VOLTAGE Horsepovver

746 X po"''er factor (Actual)

Power factor

L3

L3

230or480V

r

Ii

I,·'

P3

watts (read on meter)

= -measured --------­ volts X measured amps

THREE-PHASE VOLTAGE IMBALANCE AND CURRENT IMBALANCE FORMULAS

If the phases are unbalanced, each of the phases w·ill differ fro1n the others: Formulas:

maxin1um deviation from average voltage -------------- X 100 average voltage The maxin1u1n voltage deviation is 2% Percentage current deviation

=

maximum deviation from average current -------------- X 100 average current The max:imu1n current deviation is 10%

THREE-PHASE DELTA LOADS Three-phase balanced loads

=

Pl + P2 + P3

= total po,-ver (balanced load)

= Vr� + rf + (Ii x I2 ) IL2 = Y1� + 1� + U2 X 13) IL3 = YI� + II + (I i X 13) TL 1

Percentage voltage deviation

Total line current

,

L2

L2

volts X a1nps X efficiency = --- - - ----

P

USING WATTS TO MEASURE AIRFLOW IN ELECTRIC FURNACES The upper formula is for single-phase furnaces. The Jo·wer formula is for three-phase, delta \.Vired furnaces. volts X amps X 3.413 CFM =-------"' 0 CFN1

=

1. 8 X temperature rise 1.73 X volts X amps X 3.413 --------1.08 X temperature rise*

"'Difference between return and supply air temperatures.

HVACR FORMULAS

571

ELECTRICAL FORMULAS FOR CALCULATING AMPERES, HORSEPOWER, KILOWATTS, AND KV A ALTERNATING CURRENT

TO FIND

DIRECT CURRENT

SINGLE PHASE

TWO PHASE-FOUR WIRE

THREE PHASE

AMPERES WHEN"HP" ISI

TRANSFORMER

---

CLOSING (MAKE) OPENING (BREAK)

THERMAL CUTOUT

THERMOCOUPLE

DOUBLE THROW DOUBLE POLE

PUSH BUTTON (SPRING RETURN)

I

ACTUATING DEVICE

A.

A.

;--

VISUAL SIGNALING DEVICE '/ �

� /

'-

PILOT (TYPICAL) * ADD LETTER DESIGNATION

Ll

N

LP

CR 3

HP

IFR 4

C IFM

2

HR

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EH

3

1

HL

CR 4

CR

6

OFM

CH

5

4

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24V

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6

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R

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